PU Foam · grade
PU Foam FLEX-25
Properties of the FLEX-25 condition, compared with the other PU Foam grades.
General cushioning, packaging and furniture padding; cheapest open-cell PU.
What is PU Foam FLEX-25?
PU Foam FLEX-25 is PU Foam in the FLEX-25 grade — general cushioning, packaging and furniture padding; cheapest open-cell PU. PU Foam FLEX-25 has a tensile strength of 0.12 MPa (0.0174 ksi), weaker than 100% of polyurethane grades. Elongation at break is 150% and the elastic modulus is 0.01 GPa (0.0013 Msi). PU Foam FLEX-25 has a density of 0.03 g/cm³ (9.03×10⁻⁴ lb/in³), lighter than 100% of polyurethane grades. Its glass-transition temperature is 120°C (248 °F). RIGID-40 is the default condition FabDigit quotes; FLEX-25 is available on request or by drawing note.
Advantages
- Lightweight — 0.03 g/cm³ (9.03×10⁻⁴ 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 — 90°C (194 °F), better than 83% of polyurethane grades
- Ductile — tolerates forming and impact — 150%, better than 78% of polyurethane grades
Limitations
- Needs corrosion protection — 60/100, worse than 97% of polyurethane grades
- Poor heat conductor — 0.04 W/m·K (0.0231 BTU/hr·ft·°F), worse than 96% 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
- High mold shrinkage — 0.6%, worse than 75% of polyurethane grades
PU Foam FLEX-25 properties
Typical room-temperature values for PU Foam FLEX-25 — 9 properties are specific to this condition; the rest are grade-level values shared by every PU Foam grade. Each bar shows where the value sits among the polyurethane grades in FabDigit's library — further right is higher.
Physical4
PU Foam FLEX-25 has a density of 0.03 g/cm³ (9.03×10⁻⁴ lb/in³), lighter than 100% of polyurethane grades. Its glass-transition temperature is 120°C (248 °F).
Mechanical9
PU Foam FLEX-25 has a tensile strength of 0.12 MPa (0.0174 ksi), weaker than 100% of polyurethane grades. Elongation at break is 150% and the elastic modulus is 0.01 GPa (0.0013 Msi).
Thermal8
PU Foam FLEX-25 is rated for continuous service to 90°C (194 °F). It conducts heat at 0.04 W/m·K (0.0231 BTU/hr·ft·°F), worse than 96% of polyurethane grades. Thermal expansion is 60 µm/m·K (33.3 µin/in·°F).
Electrical4
PU Foam FLEX-25 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 FLEX-25 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 FLEX-25's machinability is excellent (92/100, better than 100% of polyurethane grades).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other PU Foam grades and fills
PU Foam is also supplied in 11 other conditions. The full side-by-side table is on the PU Foam overview.
- 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
Working with PU Foam FLEX-25
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.
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.
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) | — |
PU Foam FLEX-25 — frequently asked
What is PU Foam FLEX-25 used for?
PU Foam FLEX-25 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 FLEX-25?
PU Foam FLEX-25 has a typical tensile strength of 0.12 MPa (0.0174 ksi) — weaker than 100% of polyurethane grades. Strength varies by condition: see the 12 listed tempers.
Is PU Foam FLEX-25 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 FLEX-25 be welded?
Thermoset — cannot be welded; join by PU adhesives, foam-in-place bonding or hot-melt.
What surface finishes work on PU Foam FLEX-25?
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 FLEX-25 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 FLEX-25?
PU Foam FLEX-25 is rated for continuous use to about 90°C (194 °F), and briefly to 150°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.