Polyurethane
PU Foam
Properties, grades, machining, finishes and uses — values shown for the RIGID-40 condition.
PU Foam is a cellular polyurethane, rigid or flexible, produced by two-component reaction moulding for cushioning, insulation and lightweight tooling and pattern work; conditions include RIGID-30/40/60/HD, TOOL-500, FR, PIR, FLEX-25, FLEX-HR, viscoelastic memory, integral-skin and microcellular.
Reference datasheet — PU Foam is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
What is PU Foam?
PU Foam is a cellular polyurethane, rigid or flexible, produced by two-component reaction moulding for cushioning, insulation and lightweight tooling and pattern work; conditions include RIGID-30/40/60/HD, TOOL-500, FR, PIR, FLEX-25, FLEX-HR, viscoelastic memory, integral-skin and microcellular. The default 0.04 g/cm³ rigid grade gives 0.35 MPa tensile strength, 0.024 W/m·K thermal conductivity and service to 100 °C, making it the lowest-cost route to insulating or shock-absorbing volume. Strength is very low, it is a non-weldable thermoset, and open-cell surfaces must be sealed before paint. Use RPU tooling board grades where machinable stiffness matters. PU Foam has a density of 0.04 g/cm³ (0.0014 lb/in³), lighter than 100% of polyurethane grades. Its glass-transition temperature is 120°C (248 °F). PU Foam has a tensile strength of 0.35 MPa (0.0508 ksi), weaker than 100% of polyurethane grades. Elongation at break is 7% and the elastic modulus is 0.01 GPa (0.0013 Msi).
What is PU Foam used for?
- Cushioning/padding
- Thermal insulation
- Lightweight tooling/pattern blocks
- Packaging
Advantages
- Lightweight — 0.04 g/cm³ (0.0014 lb/in³), better than 100% of polyurethane grades
- Easy to machine — 92/100, better than 100% of polyurethane grades
- Low embodied carbon — 4.5 kg CO₂/kg, better than 100% of polyurethane grades
- High service temperature — 100°C (212 °F), better than 89% of polyurethane grades
Limitations
- Poor heat conductor — 0.02 W/m·K (0.0139 BTU/hr·ft·°F), worse than 100% of polyurethane grades
- Needs corrosion protection — 60/100, worse than 97% of polyurethane grades
- Absorbs moisture — dry before molding — 2%, worse than 96% of polyurethane grades
- Low stiffness — 0.01 GPa (0.0013 Msi), worse than 83% of polyurethane grades
- Limited ductility — 7%, worse than 78% of polyurethane grades
PU Foam properties
Typical room-temperature values for PU Foam-RIGID-40 (standard insulation / sandwich-core density: best thermal performance per cost), compiled from standards, handbooks and producer data. Each bar shows where the value sits among the polyurethane grades in FabDigit's library — further right is higher. Other conditions have their own pages: see tempers.
Physical4
PU Foam has a density of 0.04 g/cm³ (0.0014 lb/in³), lighter than 100% of polyurethane grades. Its glass-transition temperature is 120°C (248 °F).
Mechanical9
PU Foam has a tensile strength of 0.35 MPa (0.0508 ksi), weaker than 100% of polyurethane grades. Elongation at break is 7% and the elastic modulus is 0.01 GPa (0.0013 Msi).
Thermal8
PU Foam is rated for continuous service to 100°C (212 °F). It conducts heat at 0.02 W/m·K (0.0139 BTU/hr·ft·°F), worse than 100% of polyurethane grades. Thermal expansion is 60 µm/m·K (33.3 µin/in·°F).
Electrical4
PU Foam has an electrical resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental3
Corrosion resistance is good (60/100), worse than 97% of polyurethane grades. UV resistance is poor.
Sustainability4
Producing a kilogram of PU Foam takes about 110 MJ of energy and emits 4.5 kg of CO₂ — more than 83% of polyurethane grades. Typical recycled content is 3%.
Manufacturability3
PU Foam's machinability is excellent (92/100, better than 100% of polyurethane grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
PU Foam grades and fills
PU Foam is supplied in 12 conditions, each with its own property set. Open one for its full datasheet. RIGID-40 is what FabDigit quotes unless the drawing says otherwise.
- RIGID-40DefaultStandard insulation / sandwich-core density: best thermal performance per cost.0.35 MPa tensile
- TOOL-500CNC-machinable pattern, styling model and vacuum-forming tool material; fine cell, dimensionally stable.9 MPa tensile
- MICROHigh-load spring/bump-stop and vibration isolation elements (e.g. suspension jounce bumpers, machine mounts).6 MPa tensile
- INT-SKINMoulded parts needing a tough finished skin without painting: steering wheels, armrests, handles, seat pads.4 MPa tensile
- RIGID-HDUse for local load introduction, hardpoints in sandwich panels and thermal break blocks.3 MPa tensile
- RIGID-60Pick when the foam must carry compressive or sandwich shear load (marine/rail cores, pipe supports).0.65 MPa tensile
- FLEX-25General cushioning, packaging and furniture padding; cheapest open-cell PU.0.12 MPa tensile
5 further conditions are listed below with a summary only.
| Condition | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
RIGID-40Default Rigid closed-cell PUR, ~40 kg/m³ (panel / spray insulation) | Standard insulation / sandwich-core density: best thermal performance per cost. | — | 0.35 | — | — | 0.02 W/m·K |
Rigid low-density PUR, ~30 kg/m³ | Lowest-cost pour/spray insulation where only thermal performance matters, not load bearing. | — | 0.25 | — | — | 0.02 W/m·K |
Rigid PUR, ~60 kg/m³ (structural core) | Pick when the foam must carry compressive or sandwich shear load (marine/rail cores, pipe supports). | — | 0.65 | — | — | 0.03 W/m·K |
High-density rigid PUR, 100–200 kg/m³ (insert / load-bearing block) | Use for local load introduction, hardpoints in sandwich panels and thermal break blocks. | — | 3 | — | 25 Shore D | 0.04 W/m·K |
PU modelling/tooling board, ~500 kg/m³ | CNC-machinable pattern, styling model and vacuum-forming tool material; fine cell, dimensionally stable. | — | 9 | — | 62 Shore D | 0.11 W/m·K |
Flame-retardant rigid PUR (B1 / UL 94 HF-1) | Building-code and rail/transport applications requiring EN 13501 B-s1,d0 or GB 8624 B1. | — | — | — | — | 0.02 W/m·K |
Polyisocyanurate (PIR) rigid foam | Higher isocyanate index gives better fire performance and higher temperature limit than plain PUR. | — | — | — | — | 0.02 W/m·K |
Flexible open-cell slabstock, ~25 kg/m³ | General cushioning, packaging and furniture padding; cheapest open-cell PU. | — | 0.12 | 150 | — | 0.04 W/m·K |
High-resilience flexible foam, ~45 kg/m³ | Seating and mattress cores needing high resilience, durability and low fatigue. | — | 0.15 | 140 | — | 0.04 W/m·K |
Viscoelastic (memory) foam, ~55 kg/m³ | Pressure-distributing slow-recovery foam for mattresses, medical supports and vibration damping. | — | 0.09 | 120 | — | 0.04 W/m·K |
Integral-skin / self-skinning semi-rigid foam | Moulded parts needing a tough finished skin without painting: steering wheels, armrests, handles, seat pads. | — | 4 | 140 | 65 Shore A | — |
Microcellular PU elastomer foam (cellular urethane) | High-load spring/bump-stop and vibration isolation elements (e.g. suspension jounce bumpers, machine mounts). | — | 6 | 250 | 60 Shore A | — |
Working with PU Foam
Is PU Foam easy to machine?
Cuts easily with hot wire, band knife or CNC router at high feed and low chip load; use sharp upcut tools and strong dust extraction (fine dust is a respiratory hazard).
Can PU Foam be welded?
Thermoset — cannot be welded; join by PU adhesives, foam-in-place bonding or hot-melt.
Can PU Foam be formed, bent or molded?
Two-component reaction mix (pour-in-place, spray, RIM or slabstock); control mix ratio, mold temperature 35–60 °C and demold time, and vent tools to avoid voids and density gradients.
Strength versus weight in the polyurethane family
Yield strength against density for every polyurethane grade FabDigit runs. PU Foam is highlighted; hover a dot for its name, or open the interactive family chart.
PU Foam chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| polymeric MDI (4,4'-diphenylmethane diisisocyanate side; TDI used for flexible slabstock | 40 – 60 | 50 |
| blowing agentwater (CO2), cyclopentane or HFO-1233zd depending on generation | 1 – 8 | 4 |
| silicone surfactantcell stabilizer | 1 – 3 | 2 |
| amine/tin catalysts | 0.3 – 2 | 1 |
| flame retardantTCPP/phosphate esters in FR grades only | 0 – 15 | 0 |
| polyether/polyester polyolpolyol blend, includes chain extenders and crosslinkers | ≥ 35 (balance) | — |
What surface finishes work on PU Foam?
Skin can be filled and sanded then sealed/primed for painting; open-cell foam needs a surface sealer; unpainted aromatic PU yellows in sunlight so UV-stable topcoat or aliphatic skin is required.
Equivalent designations
Standards and trade names that resolve to PU Foam in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Also called
How much does PU Foam cost?
PU Foam is a standard-cost polyurethane ($$), cheaper than about 72% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
PU Foam — frequently asked
What is PU Foam used for?
PU Foam is typically used for cushioning/padding, thermal insulation, lightweight tooling/pattern blocks and packaging. In short: lowest thermal conductivity here; widest rigid-to-flexible range; fastest material to machine.
What is the tensile strength of PU Foam?
PU Foam has a typical tensile strength of 0.35 MPa (0.0508 ksi) — weaker than 100% of polyurethane grades. Strength varies by condition: see the 12 listed tempers.
Is PU Foam easy to machine?
Yes — machinability is rated excellent (92/100, better than 100% of polyurethane grades). Cuts easily with hot wire, band knife or CNC router at high feed and low chip load; use sharp upcut tools and strong dust extraction (fine dust is a respiratory hazard).
Can PU Foam be welded?
Thermoset — cannot be welded; join by PU adhesives, foam-in-place bonding or hot-melt.
What surface finishes work on PU Foam?
Skin can be filled and sanded then sealed/primed for painting; open-cell foam needs a surface sealer; unpainted aromatic PU yellows in sunlight so UV-stable topcoat or aliphatic skin is required.
Can PU Foam be formed, bent or molded?
Two-component reaction mix (pour-in-place, spray, RIM or slabstock); control mix ratio, mold temperature 35–60 °C and demold time, and vent tools to avoid voids and density gradients.
What is the maximum service temperature of PU Foam?
PU Foam is rated for continuous use to about 100°C (212 °F), and briefly to 150°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does PU Foam cost?
PU Foam is a standard-cost polyurethane ($$), cheaper than about 72% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM D1621 / D1622 / D1623 — Rigid Cellular Plastics Compression, Density, Tensile — ASTM (2020)
- ASTM D3574 — Flexible Cellular Materials, Slab/Bonded/Molded Urethane Foams — ASTM (2022)
- EN 826 / EN 12667 / EN 13165 — Thermal insulating products, rigid polyurethane — CEN (2016)
- Engineered Materials Handbook Vol.2 — Engineering Plastics (cellular polyurethanes) — ASM International (1988)
- Rigid PUR/PIR panel, spray foam and tooling board datasheets — Covestro / BASF / Huntsman / Sika (Axson) / Obo-Werke (2023)
- CES / Ashby material property charts — polymer foams — Granta (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.