{
  "schema_version": "0.1.0",
  "generated": "2026-06-09",
  "description": "Engineering material properties for design comparison. Canonical SI. Values are condition-specific (temper, grade, as-printed) and each entry declares its basis: typical handbook values, ASTM spec minimums, NDS allowable design values, or concrete specified strength. These are NOT interchangeable kinds of numbers -- read the basis before comparing. FDM entries are as-printed properties (100% infill, quality TDS-class values), not bulk polymer; expect +/-20% across brands and process. Prices are order-of-magnitude small-quantity retail, for ranking only.",
  "materials": [
    {
      "id": "al-5052-h32",
      "name": "5052-H32 aluminum",
      "category": "metal",
      "family": "aluminum",
      "condition": "H32 (strain-hardened, stabilized) sheet",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Rolled sheet has slight directionality (bend allowances differ with vs across grain) but is treated as isotropic for strength."
      },
      "properties": {
        "density_kg_m3": 2680,
        "elastic_modulus_gpa": 70.3,
        "shear_modulus_gpa": 25.9,
        "poissons_ratio": 0.33,
        "yield_strength_mpa": 193,
        "tensile_strength_mpa": 228,
        "elongation_break_pct": 12,
        "hardness": {
          "scale": "HB",
          "value": 60
        },
        "cte_um_m_k": 23.8,
        "thermal_conductivity_w_m_k": 138,
        "max_service_temp_c": 150,
        "melting_point_c": 607,
        "price_usd_kg": 7
      },
      "notes": "The formable marine alloy: tanks, spray rails, consoles, bent brackets. Best fatigue strength of the common sheet alloys and excellent saltwater corrosion resistance. Bends tighter than 6061-T6 without cracking; not heat-treatable, so welds cost little strength.",
      "confidence": "high",
      "sources": [
        "ASM Handbook Vol 2, typical wrought values",
        "ASTM B209"
      ]
    },
    {
      "id": "al-5086-h116",
      "name": "5086-H116 aluminum",
      "category": "metal",
      "family": "aluminum",
      "condition": "H116 (strain-hardened, exfoliation-resistant) plate",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Plate treated as isotropic. The number that actually changes is as-welded strength, not direction."
      },
      "properties": {
        "density_kg_m3": 2660,
        "elastic_modulus_gpa": 71,
        "poissons_ratio": 0.33,
        "yield_strength_mpa": 207,
        "tensile_strength_mpa": 290,
        "elongation_break_pct": 12,
        "cte_um_m_k": 23.8,
        "thermal_conductivity_w_m_k": 125,
        "max_service_temp_c": 65,
        "melting_point_c": 585,
        "price_usd_kg": 7.5
      },
      "notes": "Workboat hull plate. H116 per ASTM B928 resists exfoliation and intergranular corrosion in seawater. Because it is strain-hardened (not heat-treated), it keeps most of its strength as-welded (~240 MPa UTS weld-zone design basis) -- the core reason welded aluminum boats are 5xxx, not 6xxx. Keep sustained service below ~65C: high-Mg 5xxx alloys sensitize and become prone to stress corrosion cracking when held hot.",
      "confidence": "high",
      "sources": [
        "ASTM B928",
        "ASM Handbook Vol 2",
        "AWS D1.2 as-welded design values"
      ]
    },
    {
      "id": "al-5083-h116",
      "name": "5083-H116 aluminum",
      "category": "metal",
      "family": "aluminum",
      "condition": "H116 plate",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Plate treated as isotropic; as-welded knockdown is the number that matters (see notes)."
      },
      "properties": {
        "density_kg_m3": 2660,
        "elastic_modulus_gpa": 70.3,
        "poissons_ratio": 0.33,
        "yield_strength_mpa": 215,
        "tensile_strength_mpa": 305,
        "elongation_break_pct": 12,
        "cte_um_m_k": 23.8,
        "thermal_conductivity_w_m_k": 117,
        "max_service_temp_c": 65,
        "melting_point_c": 570,
        "price_usd_kg": 8
      },
      "notes": "Strongest of the common non-heat-treatable marine alloys; the default for larger welded vessels and cryogenic tanks. Same story as 5086: welds keep ~270 MPa UTS, same >65C sensitization caveat.",
      "confidence": "high",
      "sources": [
        "ASTM B928",
        "ASM Handbook Vol 2"
      ]
    },
    {
      "id": "al-6061-t6",
      "name": "6061-T6 aluminum",
      "category": "metal",
      "family": "aluminum",
      "condition": "T6 (solution treated + artificially aged)",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic, but NOT weld-stable: the heat-affected zone loses the T6 temper. As-welded design strength drops to ~165 MPa UTS unless re-aged."
      },
      "properties": {
        "density_kg_m3": 2700,
        "elastic_modulus_gpa": 68.9,
        "shear_modulus_gpa": 26,
        "poissons_ratio": 0.33,
        "yield_strength_mpa": 276,
        "tensile_strength_mpa": 310,
        "elongation_break_pct": 12,
        "hardness": {
          "scale": "HB",
          "value": 95
        },
        "cte_um_m_k": 23.6,
        "thermal_conductivity_w_m_k": 167,
        "max_service_temp_c": 150,
        "melting_point_c": 582,
        "price_usd_kg": 6.5
      },
      "notes": "The default aluminum: cheap, everywhere, machines beautifully, extrudes into everything. Use it bolted or machined; if the structure is welded and the welds are loaded, 5086/5083 usually win despite lower book numbers -- the HAZ knockdown is the trap.",
      "confidence": "high",
      "sources": [
        "ASM Handbook Vol 2",
        "ASTM B221"
      ]
    },
    {
      "id": "al-6063-t5",
      "name": "6063-T5 aluminum",
      "category": "metal",
      "family": "aluminum",
      "condition": "T5 (cooled from extrusion + artificially aged)",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Extrusions are mildly textured along the extrusion axis; treated as isotropic in practice."
      },
      "properties": {
        "density_kg_m3": 2700,
        "elastic_modulus_gpa": 68.9,
        "yield_strength_mpa": 145,
        "tensile_strength_mpa": 186,
        "elongation_break_pct": 12,
        "hardness": {
          "scale": "HB",
          "value": 60
        },
        "cte_um_m_k": 23.4,
        "thermal_conductivity_w_m_k": 209,
        "max_service_temp_c": 150,
        "melting_point_c": 616,
        "price_usd_kg": 6
      },
      "notes": "The architectural/extrusion alloy: window frames, rails, trim, heatsinks (note the conductivity). Takes a much better anodized finish than 6061 and extrudes thinner walls; meaningfully weaker, so it is a finish-and-form choice, not a structural one. T-slot framing is typically the closely related 6105-T5.",
      "confidence": "high",
      "sources": [
        "ASM Handbook Vol 2",
        "ASTM B221"
      ]
    },
    {
      "id": "al-7075-t6",
      "name": "7075-T6 aluminum",
      "category": "metal",
      "family": "aluminum",
      "condition": "T6",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Thick plate has measurable short-transverse weakness (stress-corrosion in Z of the plate) -- the one wrought alloy here where plate direction can genuinely bite."
      },
      "properties": {
        "density_kg_m3": 2810,
        "elastic_modulus_gpa": 71.7,
        "shear_modulus_gpa": 26.9,
        "poissons_ratio": 0.33,
        "yield_strength_mpa": 503,
        "tensile_strength_mpa": 572,
        "elongation_break_pct": 11,
        "hardness": {
          "scale": "HB",
          "value": 150
        },
        "cte_um_m_k": 23.6,
        "thermal_conductivity_w_m_k": 130,
        "max_service_temp_c": 120,
        "melting_point_c": 477,
        "price_usd_kg": 13
      },
      "notes": "Aircraft aluminum: yield strength of mild steel at a third the density. Practically unweldable by fusion, poor bare corrosion resistance (anodize or alclad it), pricier. Fixtures, tooling plate, highly-loaded machined parts.",
      "confidence": "high",
      "sources": [
        "ASM Handbook Vol 2",
        "ASTM B209"
      ]
    },
    {
      "id": "steel-a36",
      "name": "A36 structural steel",
      "category": "metal",
      "family": "steel",
      "condition": "hot-rolled plate / shapes, as-rolled",
      "basis": "spec_minimum",
      "anisotropy": {
        "class": "isotropic",
        "note": "Treated isotropic. Through-thickness (Z) properties of thick plate are the exception -- lamellar tearing in heavily-welded T-joints."
      },
      "properties": {
        "density_kg_m3": 7850,
        "elastic_modulus_gpa": 200,
        "shear_modulus_gpa": 79,
        "poissons_ratio": 0.3,
        "yield_strength_mpa": 250,
        "tensile_strength_mpa": 400,
        "elongation_break_pct": 20,
        "hardness": {
          "scale": "HB",
          "value": 135
        },
        "cte_um_m_k": 11.7,
        "thermal_conductivity_w_m_k": 50,
        "melting_point_c": 1425,
        "price_usd_kg": 2
      },
      "notes": "The baseline structural metal. These are certified MINIMUMS (Fy 250 / Fu 400-550 band); mill certs typically run 280-320 MPa yield. Welds with anything, forgives everything, rusts immediately. Note E: three times stiffer than any aluminum, same stiffness as fancy steels -- alloying buys strength, never stiffness.",
      "confidence": "high",
      "sources": [
        "ASTM A36/A36M",
        "AISC Steel Construction Manual"
      ]
    },
    {
      "id": "steel-1018-cd",
      "name": "1018 steel, cold drawn",
      "category": "metal",
      "family": "steel",
      "condition": "cold drawn bar",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Cold-drawn bar carries residual surface stresses -- machining one side relieves them and the part banana-bows. Not anisotropy, but the same 'direction matters' failure in practice."
      },
      "properties": {
        "density_kg_m3": 7870,
        "elastic_modulus_gpa": 205,
        "poissons_ratio": 0.29,
        "yield_strength_mpa": 370,
        "tensile_strength_mpa": 440,
        "elongation_break_pct": 15,
        "hardness": {
          "scale": "HB",
          "value": 126
        },
        "cte_um_m_k": 12.1,
        "thermal_conductivity_w_m_k": 51.9,
        "melting_point_c": 1495,
        "price_usd_kg": 2.5
      },
      "notes": "Machine-shop default mild steel: accurate cold-drawn sizes, decent finish, welds fine, case-hardens. The cold work is where the extra yield over A36 comes from -- anneal it or weld on it and it reverts toward ~250.",
      "confidence": "high",
      "sources": [
        "ASM Handbook Vol 1",
        "ASTM A108"
      ]
    },
    {
      "id": "steel-4140-annealed",
      "name": "4140 chromoly steel",
      "category": "metal",
      "family": "steel",
      "condition": "annealed (as commonly stocked: see notes for prehard)",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic. The variable axis for 4140 is heat treat, not direction: properties span 3x depending on quench and temper."
      },
      "properties": {
        "density_kg_m3": 7850,
        "elastic_modulus_gpa": 205,
        "shear_modulus_gpa": 80,
        "poissons_ratio": 0.29,
        "yield_strength_mpa": 417,
        "tensile_strength_mpa": 655,
        "elongation_break_pct": 26,
        "hardness": {
          "scale": "HB",
          "value": 197
        },
        "cte_um_m_k": 12.3,
        "thermal_conductivity_w_m_k": 42.6,
        "melting_point_c": 1416,
        "price_usd_kg": 3.5
      },
      "notes": "The workhorse alloy steel: shafts, pins, dies, weldment wear points. Values here are annealed; 'prehard' 4140HT (~28-32 HRC, UTS ~950 MPa) is the most common stocked form and machines fine; quench-and-temper reaches 1700+ MPa UTS. Weldable with preheat + care (it WILL harden and crack at the weld if you treat it like A36). Same E as mild steel.",
      "confidence": "high",
      "sources": [
        "ASM Handbook Vol 1",
        "ASTM A29"
      ]
    },
    {
      "id": "steel-a500c",
      "name": "A500 Gr C steel tube (HSS)",
      "category": "metal",
      "family": "steel",
      "condition": "cold-formed welded tube, shaped (square/rect)",
      "basis": "spec_minimum",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic; corners of cold-formed tube are work-hardened above the flats."
      },
      "properties": {
        "density_kg_m3": 7850,
        "elastic_modulus_gpa": 200,
        "yield_strength_mpa": 345,
        "tensile_strength_mpa": 425,
        "elongation_break_pct": 21,
        "cte_um_m_k": 11.7,
        "thermal_conductivity_w_m_k": 50,
        "melting_point_c": 1425,
        "price_usd_kg": 2.5
      },
      "notes": "Square/rect tube for weldments, frames, trailers, racking. Spec minimums; most domestic tube dual-certs B/C. Buy it for stiffness-per-dollar in bending/torsion -- closed sections embarrass angle iron.",
      "confidence": "high",
      "sources": [
        "ASTM A500/A500M",
        "AISC Steel Construction Manual"
      ]
    },
    {
      "id": "ss-304",
      "name": "304 stainless (18-8)",
      "category": "metal",
      "family": "stainless",
      "condition": "annealed",
      "basis": "spec_minimum",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic annealed; work-hardens dramatically (a dull drill bit creates a hardened zone the next bit cannot cut)."
      },
      "properties": {
        "density_kg_m3": 8000,
        "elastic_modulus_gpa": 193,
        "shear_modulus_gpa": 77,
        "poissons_ratio": 0.29,
        "yield_strength_mpa": 205,
        "tensile_strength_mpa": 515,
        "elongation_break_pct": 40,
        "cte_um_m_k": 17.2,
        "thermal_conductivity_w_m_k": 16.2,
        "melting_point_c": 1400,
        "price_usd_kg": 5
      },
      "notes": "'18-8' on a fastener = this family (302/304). Spec minimums shown; typical annealed runs ~290 yield / ~580 UTS, and cold-worked A2-70 bolts hit 450/700. Annealed yield is LOWER than mild steel -- stainless buys corrosion resistance, not strength. Huge CTE + low conductivity = weld distortion machine. Slightly magnetic when cold-worked; gauls on itself (anti-seize on stainless threads, always).",
      "confidence": "high",
      "sources": [
        "ASTM A240",
        "ISO 3506 (A2-70 fasteners)"
      ]
    },
    {
      "id": "ss-316",
      "name": "316 stainless",
      "category": "metal",
      "family": "stainless",
      "condition": "annealed",
      "basis": "spec_minimum",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic; same work-hardening behavior as 304."
      },
      "properties": {
        "density_kg_m3": 8000,
        "elastic_modulus_gpa": 193,
        "poissons_ratio": 0.28,
        "yield_strength_mpa": 205,
        "tensile_strength_mpa": 515,
        "elongation_break_pct": 40,
        "cte_um_m_k": 15.9,
        "thermal_conductivity_w_m_k": 16.3,
        "melting_point_c": 1375,
        "price_usd_kg": 7
      },
      "notes": "304 plus 2-3% molybdenum: the marine grade (A4 fasteners, deck hardware, anything that lives in salt spray). Mechanically a twin of 304 -- you pay the premium purely for pitting/crevice resistance. Still crevice-corrodes in stagnant trapped seawater (under washers, inside swage fittings).",
      "confidence": "high",
      "sources": [
        "ASTM A240",
        "ISO 3506 (A4 fasteners)"
      ]
    },
    {
      "id": "ti-6al-4v",
      "name": "Ti-6Al-4V titanium (Grade 5)",
      "category": "metal",
      "family": "titanium",
      "condition": "annealed",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Wrought annealed treated isotropic (texture exists in rolled product but is a detail at this altitude)."
      },
      "properties": {
        "density_kg_m3": 4430,
        "elastic_modulus_gpa": 113.8,
        "shear_modulus_gpa": 44,
        "poissons_ratio": 0.34,
        "yield_strength_mpa": 880,
        "tensile_strength_mpa": 950,
        "elongation_break_pct": 14,
        "hardness": {
          "scale": "HRC",
          "value": 36
        },
        "cte_um_m_k": 8.6,
        "thermal_conductivity_w_m_k": 6.7,
        "melting_point_c": 1604,
        "price_usd_kg": 40
      },
      "notes": "The specific-strength benchmark: 7075 strength at 60% the density of steel, immune to seawater. Here mostly as a calibration point -- sort by specific strength and watch it sit on top. Miserable to machine (low conductivity cooks tools), noble galvanically (fine with carbon, will eat a neighboring aluminum part).",
      "confidence": "high",
      "sources": [
        "ASM Handbook Vol 2",
        "ASTM B348 Grade 5"
      ]
    },
    {
      "id": "brass-c360",
      "name": "360 brass (free-cutting)",
      "category": "metal",
      "family": "brass",
      "condition": "H02 half-hard rod",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic."
      },
      "properties": {
        "density_kg_m3": 8500,
        "elastic_modulus_gpa": 97,
        "poissons_ratio": 0.31,
        "yield_strength_mpa": 310,
        "tensile_strength_mpa": 400,
        "elongation_break_pct": 23,
        "hardness": {
          "scale": "HRB",
          "value": 78
        },
        "cte_um_m_k": 20.5,
        "thermal_conductivity_w_m_k": 115,
        "melting_point_c": 885,
        "price_usd_kg": 9
      },
      "notes": "Machinability = 100% -- the scale every other metal is rated against. Fittings, bushings, knurled bits, anything on a lathe. Denser than steel (heft reads as quality). The lead that makes it free-cutting also makes it dezincify in seawater: use naval brass or bronze below the waterline.",
      "confidence": "medium",
      "sources": [
        "ASM Handbook Vol 2",
        "ASTM B16"
      ]
    },
    {
      "id": "concrete-1500",
      "name": "1500 psi concrete",
      "category": "concrete",
      "family": "concrete",
      "condition": "normal weight, 28-day, f'c = 1500 psi",
      "basis": "specified_strength",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic but radically asymmetric: tension capacity is ~10% of compression and is taken as ZERO in design -- that is what the rebar is for. The compressive number is the only one concrete is allowed to be proud of."
      },
      "properties": {
        "density_kg_m3": 2300,
        "elastic_modulus_gpa": 15.1,
        "poissons_ratio": 0.2,
        "compressive_strength_mpa": 10.3,
        "flexural_strength_mpa": 2.0,
        "cte_um_m_k": 10,
        "thermal_conductivity_w_m_k": 1.8,
        "price_usd_kg": 0.08
      },
      "notes": "Lean mix: mud slabs, fill, fence posts, massing. Below the ACI structural floor (2500 psi) -- spec it where the concrete is a shape, not a structure. E and flexural (modulus of rupture) computed from f'c per ACI 318 (Ec = 4700*sqrt(f'c), fr = 0.62*sqrt(f'c), MPa); real mixes scatter +/-20%. Cheapest structural-ish material on earth by mass, by far -- that is the entire argument for it.",
      "confidence": "medium",
      "sources": [
        "ACI 318-19 ch. 19",
        "PCA Design and Control of Concrete Mixtures"
      ]
    },
    {
      "id": "concrete-3500",
      "name": "3500 psi concrete",
      "category": "concrete",
      "family": "concrete",
      "condition": "normal weight, 28-day, f'c = 3500 psi",
      "basis": "specified_strength",
      "anisotropy": {
        "class": "isotropic",
        "note": "Same asymmetry as all concrete: tension ~ 8-12% of compression, designed as zero. Cracked is the normal operating state."
      },
      "properties": {
        "density_kg_m3": 2320,
        "elastic_modulus_gpa": 23.1,
        "poissons_ratio": 0.2,
        "compressive_strength_mpa": 24.1,
        "flexural_strength_mpa": 3.0,
        "cte_um_m_k": 10,
        "thermal_conductivity_w_m_k": 1.8,
        "price_usd_kg": 0.08
      },
      "notes": "The residential default: footings, slabs, driveways. E and fr per ACI 318 formulas from f'c. Spec air entrainment for anything outdoors in freeze-thaw country. Plain ~2300 kg/m3; call it 2400 reinforced. Strength quoted at 28 days -- it keeps gaining for years.",
      "confidence": "medium",
      "sources": [
        "ACI 318-19 ch. 19",
        "PCA Design and Control of Concrete Mixtures"
      ]
    },
    {
      "id": "wood-df-ss",
      "name": "Douglas fir-larch, Select Structural",
      "category": "wood",
      "family": "softwood lumber",
      "condition": "visually graded dimension lumber (2-4 in. thick), dry service",
      "basis": "nds_design",
      "anisotropy": {
        "class": "orthotropic",
        "axes": {
          "para": "parallel to grain (along the tree)",
          "perp": "perpendicular to grain (across the tree; radial/tangential collapsed)"
        },
        "note": "Wood is the textbook orthotropic material: ~15x stiffer and ~3x stronger in compression along the grain than across it, and tension perpendicular to grain is so weak (~2-3% of parallel) that NDS refuses to publish a value -- you detail connections so it never happens. Moisture movement is the same story: ~0.1% longitudinal vs 2-8% across the grain, green to dry."
      },
      "properties": {
        "density_kg_m3": 530,
        "elastic_modulus_gpa": {
          "para": 13.1,
          "perp": 0.9
        },
        "tensile_strength_mpa": {
          "para": 6.9
        },
        "compressive_strength_mpa": {
          "para": 11.7,
          "perp": 4.31
        },
        "flexural_strength_mpa": 10.3,
        "shear_strength_mpa": 1.24,
        "elongation_break_pct": 1,
        "cte_um_m_k": {
          "para": 3.5,
          "perp": 34
        },
        "thermal_conductivity_w_m_k": 0.12,
        "price_usd_kg": 1.2
      },
      "notes": "ALLOWABLE design values (NDS 2018 Table 4A: Fb 1500 / Ft 1000 / Fv 180 / Fc-perp 625 / Fc 1700 psi, E 1.9e6) -- ultimate clear-wood strength is roughly 2-3x these; do not compare raw against 'typical'-basis materials. Adjustment factors (load duration, wet service, size, repetitive member) still apply. E-perp from Wood Handbook clear-wood ratios, not NDS. Best strength-to-weight of any material here that you can buy at a lumber yard.",
      "confidence": "high",
      "sources": [
        "NDS 2018 Supplement Table 4A",
        "FPL Wood Handbook (FPL-GTR-282)"
      ]
    },
    {
      "id": "wood-df-no2",
      "name": "Douglas fir-larch, No. 2",
      "category": "wood",
      "family": "softwood lumber",
      "condition": "visually graded dimension lumber (2-4 in. thick), dry service",
      "basis": "nds_design",
      "anisotropy": {
        "class": "orthotropic",
        "axes": {
          "para": "parallel to grain",
          "perp": "perpendicular to grain"
        },
        "note": "Same orthotropy as all wood. Grade knocks down the parallel-to-grain numbers (knots interrupt the grain); perpendicular properties barely change because they were never about continuous grain."
      },
      "properties": {
        "density_kg_m3": 530,
        "elastic_modulus_gpa": {
          "para": 11.0,
          "perp": 0.76
        },
        "tensile_strength_mpa": {
          "para": 3.97
        },
        "compressive_strength_mpa": {
          "para": 9.31,
          "perp": 4.31
        },
        "flexural_strength_mpa": 6.2,
        "shear_strength_mpa": 1.24,
        "elongation_break_pct": 1,
        "cte_um_m_k": {
          "para": 3.5,
          "perp": 34
        },
        "thermal_conductivity_w_m_k": 0.12,
        "price_usd_kg": 0.7
      },
      "notes": "What the lumber yard hands you when you say '2x6'. NDS 2018 Table 4A allowables (Fb 900 / Ft 575 / Fc 1350 psi, E 1.6e6). Note bending strength drops 40% from Select Structural but stiffness only 16% -- knots break before they bend.",
      "confidence": "high",
      "sources": [
        "NDS 2018 Supplement Table 4A"
      ]
    },
    {
      "id": "glulam-24f-v4",
      "name": "Glulam 24F-V4 (DF)",
      "category": "wood",
      "family": "glulam",
      "condition": "24F-1.8E Douglas fir, unbalanced layup, dry service",
      "basis": "nds_design",
      "anisotropy": {
        "class": "orthotropic",
        "axes": {
          "para": "parallel to grain / along the member",
          "perp": "perpendicular to grain"
        },
        "note": "Wood orthotropy PLUS layup asymmetry: 24F-V4 puts its best laminations on the tension face, so bending capacity is 2400 psi one way and 1850 psi flipped. An entire beam that has a right-side-up. Camber tells you which way."
      },
      "properties": {
        "density_kg_m3": 560,
        "elastic_modulus_gpa": {
          "para": 12.4,
          "perp": 0.83
        },
        "tensile_strength_mpa": {
          "para": 7.6
        },
        "compressive_strength_mpa": {
          "para": 11.4,
          "perp": 4.48
        },
        "flexural_strength_mpa": 16.5,
        "shear_strength_mpa": 1.83,
        "cte_um_m_k": {
          "para": 3.5,
          "perp": 34
        },
        "thermal_conductivity_w_m_k": 0.13,
        "price_usd_kg": 2
      },
      "notes": "Engineered timber: defects dispersed across laminations, so allowables run ~60% above Select Structural sawn lumber and sizes are unlimited by the tree. Values are allowables (Fbx+ 2400 / Fv 265 / Fc-perp 650 psi, Ex 1.8e6); volume factor applies to big members. The mass timber gateway material.",
      "confidence": "high",
      "sources": [
        "NDS 2018 Supplement Table 5A",
        "APA EWS Y117"
      ]
    },
    {
      "id": "nylon-pa6",
      "name": "Nylon 6 (machined stock)",
      "category": "polymer",
      "family": "polyamide",
      "condition": "extruded/cast stock, dry-as-molded (see notes for conditioned)",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic in direction -- the split personality is moisture, not orientation: at 50% RH equilibrium (~3% water) stiffness roughly halves and toughness doubles vs these dry values. Design to the conditioned state the part will actually live in."
      },
      "properties": {
        "density_kg_m3": 1140,
        "elastic_modulus_gpa": 2.8,
        "yield_strength_mpa": 79,
        "tensile_strength_mpa": 79,
        "elongation_break_pct": 50,
        "flexural_strength_mpa": 110,
        "flexural_modulus_gpa": 2.8,
        "cte_um_m_k": 85,
        "thermal_conductivity_w_m_k": 0.25,
        "glass_transition_c": 50,
        "melting_point_c": 220,
        "hdt_c": 160,
        "max_service_temp_c": 100,
        "price_usd_kg": 10
      },
      "notes": "Bushings, sheaves, wear pads, hammer faces. Tough, slippery, fatigue-resistant. Absorbs up to ~3% water at equilibrium (9% saturated): dimensions grow ~0.7%, so machine generous clearances and never spec nylon for a precision fit that sees humidity swings. Acetal is the answer when that bites.",
      "confidence": "medium",
      "sources": [
        "Ensinger/Mitsubishi stock-shape datasheets",
        "CAMPUS plastics database"
      ]
    },
    {
      "id": "pc-machined",
      "name": "Polycarbonate (sheet/machined)",
      "category": "polymer",
      "family": "polycarbonate",
      "condition": "extruded sheet / machined stock",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic. The hidden axis is residual stress from extrusion: machine it hard or hit it with solvent and it crazes along the locked-in stress field. Anneal before precision machining."
      },
      "properties": {
        "density_kg_m3": 1200,
        "elastic_modulus_gpa": 2.38,
        "yield_strength_mpa": 62,
        "tensile_strength_mpa": 66,
        "elongation_break_pct": 110,
        "flexural_strength_mpa": 93,
        "flexural_modulus_gpa": 2.34,
        "cte_um_m_k": 67,
        "thermal_conductivity_w_m_k": 0.2,
        "glass_transition_c": 147,
        "hdt_c": 140,
        "max_service_temp_c": 115,
        "price_usd_kg": 8
      },
      "notes": "The impact king of clear plastics (~850 J/m notched Izod -- an order of magnitude over acrylic): machine guards, windshields, anything that must not shatter. Caveats earn their keep: notch-sensitive, crazes near solvents (no acetone, check your cleaners and adhesives), yellows in UV unless coated. Amorphous -- no melting point, it just softens past Tg.",
      "confidence": "high",
      "sources": [
        "Covestro Makrolon datasheets",
        "CAMPUS plastics database"
      ]
    },
    {
      "id": "hdpe",
      "name": "HDPE",
      "category": "polymer",
      "family": "polyethylene",
      "condition": "extruded sheet (marine board class)",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic. The number that swings is thermal: CTE ~10x steel, so a 2 m HDPE board grows ~8 mm across a 30C day-night swing. Slot your fastener holes."
      },
      "properties": {
        "density_kg_m3": 960,
        "elastic_modulus_gpa": 1.0,
        "yield_strength_mpa": 26,
        "tensile_strength_mpa": 31,
        "elongation_break_pct": 600,
        "flexural_modulus_gpa": 1.0,
        "hardness": {
          "scale": "Shore D",
          "value": 62
        },
        "cte_um_m_k": 130,
        "thermal_conductivity_w_m_k": 0.45,
        "glass_transition_c": -110,
        "melting_point_c": 130,
        "hdt_c": 75,
        "max_service_temp_c": 80,
        "price_usd_kg": 3
      },
      "notes": "Marine board (King StarBoard class), cutting boards, tanks, skids. Floats, shrugs off water and most chemistry, never rots. Nothing glues to it -- design for thermal welding or mechanical fastening. Tg of -110C is why it stays tough in a freezer.",
      "confidence": "high",
      "sources": [
        "King Plastic StarBoard TDS",
        "CAMPUS plastics database"
      ]
    },
    {
      "id": "uhmw-pe",
      "name": "UHMW-PE",
      "category": "polymer",
      "family": "polyethylene",
      "condition": "compression-molded/ram-extruded stock",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic. Creep is the directionless gotcha: sustained point loads make it flow. Use it to slide, not to clamp."
      },
      "properties": {
        "density_kg_m3": 930,
        "elastic_modulus_gpa": 0.69,
        "yield_strength_mpa": 21,
        "tensile_strength_mpa": 40,
        "elongation_break_pct": 350,
        "hardness": {
          "scale": "Shore D",
          "value": 64
        },
        "cte_um_m_k": 200,
        "thermal_conductivity_w_m_k": 0.41,
        "melting_point_c": 135,
        "max_service_temp_c": 80,
        "price_usd_kg": 5
      },
      "notes": "The abrasion champion: outwears steel in sliding-sand service. Trailer bunks, chute and hopper liners, dock edges, guide rails. Molecular weight so high it will not melt-flow (cannot injection mold or meaningfully glue it) and notched impact tests just bend. Highest CTE in this dataset -- float it in slots.",
      "confidence": "high",
      "sources": [
        "Roechling Polystone-M datasheets",
        "Mitsubishi TIVAR TDS"
      ]
    },
    {
      "id": "acetal-pom",
      "name": "Acetal / Delrin (POM-H)",
      "category": "polymer",
      "family": "acetal",
      "condition": "extruded homopolymer stock",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Isotropic and -- the point -- stays that way: lowest moisture uptake of the engineering plastics, so parts hold size in any weather. The anti-nylon."
      },
      "properties": {
        "density_kg_m3": 1410,
        "elastic_modulus_gpa": 3.1,
        "yield_strength_mpa": 70,
        "tensile_strength_mpa": 70,
        "elongation_break_pct": 30,
        "flexural_strength_mpa": 97,
        "flexural_modulus_gpa": 2.9,
        "cte_um_m_k": 105,
        "thermal_conductivity_w_m_k": 0.31,
        "glass_transition_c": -60,
        "melting_point_c": 178,
        "hdt_c": 160,
        "max_service_temp_c": 90,
        "price_usd_kg": 9
      },
      "notes": "The default precision-machining plastic: stiff, slippery, dimensionally boring (in the best way). Gears, bushings, fixture jaws, valve bodies. Homopolymer (Delrin) is a touch stronger but can have centerline porosity in thick sections; copolymer trades a little strength for none of that. Bonding is near-impossible -- design mechanical.",
      "confidence": "high",
      "sources": [
        "DuPont Delrin design guide",
        "Ensinger TECAFORM datasheets"
      ]
    },
    {
      "id": "acrylic-cast",
      "name": "Acrylic, cast (PMMA)",
      "category": "polymer",
      "family": "acrylic",
      "condition": "cell-cast sheet",
      "basis": "typical",
      "anisotropy": {
        "class": "isotropic",
        "note": "Cast sheet is isotropic and stress-free (extruded acrylic is the cheaper, stressed, harder-to-machine cousin). Brittle in every direction equally."
      },
      "properties": {
        "density_kg_m3": 1190,
        "elastic_modulus_gpa": 3.1,
        "tensile_strength_mpa": 72,
        "elongation_break_pct": 4.5,
        "flexural_strength_mpa": 105,
        "flexural_modulus_gpa": 3.0,
        "cte_um_m_k": 72,
        "thermal_conductivity_w_m_k": 0.19,
        "glass_transition_c": 105,
        "hdt_c": 98,
        "max_service_temp_c": 80,
        "price_usd_kg": 6
      },
      "notes": "Optically the best plastic, UV-stable outdoors for decades without coatings (where PC yellows), and solvent-cements into invisible joints. The trade: brittle and notch-sensitive -- drill with plastic-point bits, deburr everything, never quench-cool. Stiffest clear material here; choose PC instead the moment impact enters the spec.",
      "confidence": "high",
      "sources": [
        "Plaskolite/Perspex cast acrylic TDS",
        "CAMPUS plastics database"
      ]
    },
    {
      "id": "fdm-pla",
      "name": "PLA (printed)",
      "category": "fdm",
      "family": "polylactide",
      "condition": "as-printed, 100% infill, 0.2 mm layers",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane (along extruded beads)",
          "z": "across layer bonds (build direction)"
        },
        "note": "Every FDM part is a laminate: Z strength is the strength of remelted weld lines, here ~75% of XY -- one of the better ratios in FDM, and PLA's saving grace. Z elongation is roughly half XY; parts snap at layer lines under bending. Orient the load path into the layer plane."
      },
      "properties": {
        "density_kg_m3": 1240,
        "elastic_modulus_gpa": 2.7,
        "tensile_strength_mpa": {
          "xy": 50,
          "z": 38
        },
        "elongation_break_pct": 3,
        "flexural_strength_mpa": 80,
        "flexural_modulus_gpa": 2.9,
        "cte_um_m_k": 68,
        "thermal_conductivity_w_m_k": 0.13,
        "glass_transition_c": 60,
        "melting_point_c": 175,
        "hdt_c": 56,
        "max_service_temp_c": 50,
        "price_usd_kg": 22
      },
      "printing": {
        "nozzle_c": [
          200,
          230
        ],
        "bed_c": [
          50,
          60
        ],
        "chamber": "open",
        "dry_before_use": false,
        "abrasive": false
      },
      "notes": "Stiffest and easiest of the commodity filaments, prints gorgeous, costs nothing. Then summer happens: parts soften from 55C (a closed car kills it) and it creeps under sustained load worse than anything else here. Annealing buys ~30C of heat tolerance for some shrink/warp. Prototypes, jigs that live indoors, anything visual.",
      "confidence": "high",
      "sources": [
        "Prusament PLA TDS (XY/Z tensile)",
        "Polymaker PolyLite PLA TDS"
      ]
    },
    {
      "id": "fdm-petg",
      "name": "PETG (printed)",
      "category": "fdm",
      "family": "copolyester",
      "condition": "as-printed, 100% infill, 0.2 mm layers",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane",
          "z": "across layer bonds"
        },
        "note": "Best layer adhesion of the commodity set: Z holds ~85% of XY strength. The anisotropy you feel instead is ductility -- XY tears gradually, Z still pops."
      },
      "properties": {
        "density_kg_m3": 1270,
        "elastic_modulus_gpa": 1.7,
        "tensile_strength_mpa": {
          "xy": 47,
          "z": 40
        },
        "elongation_break_pct": 8,
        "flexural_strength_mpa": 68,
        "flexural_modulus_gpa": 1.8,
        "cte_um_m_k": 60,
        "thermal_conductivity_w_m_k": 0.2,
        "glass_transition_c": 80,
        "hdt_c": 70,
        "max_service_temp_c": 65,
        "price_usd_kg": 22
      },
      "printing": {
        "nozzle_c": [
          230,
          255
        ],
        "bed_c": [
          70,
          85
        ],
        "chamber": "open",
        "dry_before_use": true,
        "abrasive": false
      },
      "notes": "The functional-part default on an open printer: tougher and more heat- and chemical-tolerant than PLA, near-isotropic layer bonding, slightly flexy. Strings like a violin and welds itself to bare PEI sheets (glue stick as a release layer). Amorphous, no true melting point. Outdoor-capable short-term; ASA for years in the sun.",
      "confidence": "high",
      "sources": [
        "Prusament PETG TDS (XY/Z tensile)",
        "Polymaker PolyLite PETG TDS"
      ]
    },
    {
      "id": "fdm-pctg",
      "name": "PCTG (printed)",
      "category": "fdm",
      "family": "copolyester",
      "condition": "as-printed, 100% infill, 0.2 mm layers",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane",
          "z": "across layer bonds"
        },
        "note": "Layer adhesion as good as PETG or better (~85-90% Z/XY), and enough ductility that Z failures bend-then-break instead of snapping."
      },
      "properties": {
        "density_kg_m3": 1230,
        "elastic_modulus_gpa": 1.6,
        "tensile_strength_mpa": {
          "xy": 50,
          "z": 44
        },
        "elongation_break_pct": 120,
        "flexural_strength_mpa": 70,
        "flexural_modulus_gpa": 1.7,
        "glass_transition_c": 78,
        "hdt_c": 68,
        "max_service_temp_c": 60,
        "price_usd_kg": 30
      },
      "printing": {
        "nozzle_c": [
          250,
          270
        ],
        "bed_c": [
          75,
          90
        ],
        "chamber": "open",
        "dry_before_use": true,
        "abrasive": false
      },
      "notes": "PETG's tougher sibling (higher comonomer ratio): several times the impact strength, huge elongation, clearer, less brittle in Z. Snap-fits, guards, parts that get dropped. Runs ~20C hotter than PETG. Per-brand spread is wider than PETG -- check the actual TDS.",
      "confidence": "medium",
      "sources": [
        "Extrudr PCTG TDS",
        "Essentium PCTG TDS"
      ]
    },
    {
      "id": "fdm-abs",
      "name": "ABS (printed)",
      "category": "fdm",
      "family": "styrenic",
      "condition": "as-printed, 100% infill, 0.2 mm layers, enclosed",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane",
          "z": "across layer bonds"
        },
        "note": "Z holds ~70% of XY at best, and only with a hot chamber -- print ABS cold and layer bonds drop below half. Acetone vapor smoothing partially heals the laminate (it literally re-welds the surface)."
      },
      "properties": {
        "density_kg_m3": 1040,
        "elastic_modulus_gpa": 2.1,
        "tensile_strength_mpa": {
          "xy": 40,
          "z": 28
        },
        "elongation_break_pct": 10,
        "flexural_strength_mpa": 62,
        "flexural_modulus_gpa": 2.2,
        "cte_um_m_k": 90,
        "thermal_conductivity_w_m_k": 0.17,
        "glass_transition_c": 105,
        "hdt_c": 95,
        "max_service_temp_c": 85,
        "price_usd_kg": 20
      },
      "printing": {
        "nozzle_c": [
          250,
          270
        ],
        "bed_c": [
          95,
          110
        ],
        "chamber": "recommended",
        "dry_before_use": false,
        "abrasive": false
      },
      "notes": "The legacy engineering filament: real heat tolerance, post-machines and glues well, acetone-smooths and solvent-welds. Warps off the bed without an enclosure and the styrene fumes want ventilation. ASA has eaten most of its use cases except acetone work.",
      "confidence": "high",
      "sources": [
        "Bambu Lab ABS TDS",
        "Polymaker PolyLite ABS TDS"
      ]
    },
    {
      "id": "fdm-asa",
      "name": "ASA (printed)",
      "category": "fdm",
      "family": "styrenic",
      "condition": "as-printed, 100% infill, 0.2 mm layers, enclosed",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane",
          "z": "across layer bonds"
        },
        "note": "Same laminate behavior as ABS: ~70% Z/XY with a warm chamber, worse without. Orient outdoor load-bearing prints so sun-facing stress runs in the layer plane."
      },
      "properties": {
        "density_kg_m3": 1070,
        "elastic_modulus_gpa": 2.0,
        "tensile_strength_mpa": {
          "xy": 43,
          "z": 30
        },
        "elongation_break_pct": 9,
        "flexural_strength_mpa": 65,
        "flexural_modulus_gpa": 2.1,
        "cte_um_m_k": 98,
        "thermal_conductivity_w_m_k": 0.17,
        "glass_transition_c": 102,
        "hdt_c": 96,
        "max_service_temp_c": 85,
        "price_usd_kg": 28
      },
      "printing": {
        "nozzle_c": [
          250,
          270
        ],
        "bed_c": [
          95,
          110
        ],
        "chamber": "recommended",
        "dry_before_use": true,
        "abrasive": false
      },
      "notes": "UV-stable ABS -- the outdoor filament. Brackets, trailer and boat fittings, enclosures that live in weather: ASA keeps color and toughness where ABS chalks and PLA dies. Slightly less warp-prone than ABS, still wants the enclosure. Acetone-workable.",
      "confidence": "high",
      "sources": [
        "Prusament ASA TDS",
        "Polymaker PolyLite ASA TDS"
      ]
    },
    {
      "id": "fdm-pa6-cf",
      "name": "CF nylon, PA6-CF (printed)",
      "category": "fdm",
      "family": "polyamide, carbon-filled",
      "condition": "as-printed, 100% infill, dried filament, dry-as-printed values",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane, beads + fibers aligned",
          "z": "across layer bonds"
        },
        "note": "The most anisotropic material in this dataset. Chopped fibers align with the extruded bead, so XY stiffness is ~2.4x Z and XY strength ~2.5x Z -- the fibers reinforce exactly the directions that were already strong and do nothing for the weld lines. Treat Z like a glue joint in a part that is otherwise aluminum-adjacent."
      },
      "properties": {
        "density_kg_m3": 1190,
        "elastic_modulus_gpa": {
          "xy": 6.0,
          "z": 2.5
        },
        "tensile_strength_mpa": {
          "xy": 95,
          "z": 38
        },
        "elongation_break_pct": 3,
        "flexural_strength_mpa": 120,
        "flexural_modulus_gpa": 5.0,
        "cte_um_m_k": {
          "xy": 20,
          "z": 70
        },
        "glass_transition_c": 65,
        "melting_point_c": 220,
        "hdt_c": 175,
        "max_service_temp_c": 110,
        "price_usd_kg": 70
      },
      "printing": {
        "nozzle_c": [
          280,
          310
        ],
        "bed_c": [
          80,
          100
        ],
        "chamber": "recommended",
        "dry_before_use": true,
        "abrasive": true
      },
      "notes": "The stiffness champion of practical FDM: prints jigs, fixtures, and end-use brackets that genuinely replace machined parts -- in XY. Demands respect: filament must be actively dried (wet PA prints foam), fibers eat brass nozzles (hardened steel minimum), and like all nylon it drinks water after printing too (conditioned stiffness drops ~30-40% from these dry values).",
      "confidence": "medium",
      "sources": [
        "Polymaker Fiberon PA6-CF20 TDS",
        "Bambu Lab PAHT-CF TDS"
      ]
    },
    {
      "id": "fdm-pc",
      "name": "Polycarbonate (printed)",
      "category": "fdm",
      "family": "polycarbonate",
      "condition": "as-printed, 100% infill, enclosed chamber",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane",
          "z": "across layer bonds"
        },
        "note": "~65% Z/XY in a hot chamber; on an open printer the layer bonds are dramatically worse and the part is a stack of potato chips. Printed PC keeps nothing like sheet PC's legendary impact strength -- the weld lines are notches everywhere."
      },
      "properties": {
        "density_kg_m3": 1190,
        "elastic_modulus_gpa": 2.3,
        "tensile_strength_mpa": {
          "xy": 60,
          "z": 40
        },
        "elongation_break_pct": 12,
        "flexural_strength_mpa": 90,
        "flexural_modulus_gpa": 2.3,
        "cte_um_m_k": 65,
        "glass_transition_c": 145,
        "hdt_c": 135,
        "max_service_temp_c": 110,
        "price_usd_kg": 35
      },
      "printing": {
        "nozzle_c": [
          270,
          300
        ],
        "bed_c": [
          100,
          110
        ],
        "chamber": "required",
        "dry_before_use": true,
        "abrasive": false
      },
      "notes": "Top of the unfilled-filament ladder for heat + strength together. Warps hard, shrinks hard, wants a real heated chamber. Most consumer 'PC' spools are blends that print easier and rate lower -- read the actual TDS, not the family name.",
      "confidence": "medium",
      "sources": [
        "Polymaker PC TDS",
        "Bambu Lab PC TDS"
      ]
    },
    {
      "id": "fdm-tpu-95a",
      "name": "TPU 95A (printed)",
      "category": "fdm",
      "family": "polyurethane elastomer",
      "condition": "as-printed, 100% infill",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane",
          "z": "across layer bonds"
        },
        "note": "Elastomers fuse: Z bond runs ~85% of XY, the best in FDM. The practical anisotropy is in elongation -- stretch across layers and it still lets go earlier than along them."
      },
      "properties": {
        "density_kg_m3": 1210,
        "elastic_modulus_gpa": 0.08,
        "tensile_strength_mpa": {
          "xy": 35,
          "z": 30
        },
        "elongation_break_pct": 450,
        "hardness": {
          "scale": "Shore A",
          "value": 95
        },
        "glass_transition_c": -30,
        "melting_point_c": 215,
        "max_service_temp_c": 80,
        "price_usd_kg": 35
      },
      "printing": {
        "nozzle_c": [
          225,
          245
        ],
        "bed_c": [
          40,
          60
        ],
        "chamber": "open",
        "dry_before_use": true,
        "abrasive": false
      },
      "notes": "The standard flexible: gaskets, bumpers, grips, vibration mounts, protective sleeves. 95A is 'soft for a plastic', not 'rubber band' -- thin walls flex, thick sections feel like a hockey puck. Print slow on direct drive, keep it bone dry or it bubbles into foam, and feed it around (not through) most multi-material units.",
      "confidence": "medium",
      "sources": [
        "NinjaTek Cheetah TDS",
        "Polymaker TPU95 TDS"
      ]
    },
    {
      "id": "fdm-tpu-68d",
      "name": "TPU 68D (printed)",
      "category": "fdm",
      "family": "polyurethane elastomer",
      "condition": "as-printed, 100% infill",
      "basis": "typical",
      "anisotropy": {
        "class": "transversely_isotropic",
        "axes": {
          "xy": "in the layer plane",
          "z": "across layer bonds"
        },
        "note": "Same excellent elastomer layer fusion as soft TPU (~85% Z/XY). Hard-shore TPUs behave like a tough semi-rigid plastic with a memory, in every direction."
      },
      "properties": {
        "density_kg_m3": 1200,
        "elastic_modulus_gpa": 0.4,
        "tensile_strength_mpa": {
          "xy": 45,
          "z": 38
        },
        "elongation_break_pct": 180,
        "hardness": {
          "scale": "Shore D",
          "value": 68
        },
        "melting_point_c": 220,
        "max_service_temp_c": 90,
        "price_usd_kg": 40
      },
      "printing": {
        "nozzle_c": [
          230,
          260
        ],
        "bed_c": [
          50,
          70
        ],
        "chamber": "open",
        "dry_before_use": true,
        "abrasive": false
      },
      "notes": "The semi-rigid class: between PETG and rubber. Living hinges, bump stops, rollers, casters, anything that takes impact and abuse without needing stiffness. 68D is a brand-specific designation (eSUN eTPU-68D and kin) and chemistry varies between vendors more than for any other entry here -- verify against the TDS of the actual spool.",
      "confidence": "needs_verification",
      "sources": [
        "eSUN eTPU-68D TDS",
        "BASF Ultrafuse hard-TPU family TDS"
      ]
    }
  ]
}