RPU ISF
Grade
ISF = integral-skin (self-skinning) rigid foam
Pick for one-shot mouldings that need a tough dense skin over a light core — housings, armrests, medical equipment covers.
Values for the ISF condition
Other RPU grades and fills
RPU is listed in 10 conditions; see the grade overview at RPU.
Compare all 10 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Flame-retardant rigid PU / polyisocyanurate | Pick for building panels, transport and electrical enclosures needing UL 94 V-0 or GB 8624 B1 fire performance. | — | 0.25 | 6 | — |
Rigid closed-cell insulation foam, 30–45 kg/m³ | Pick for thermal insulation of panels, pipes, cold rooms and refrigerators where the lowest λ per unit weight matters. | — | 0.28 | — | — |
Rigid structural pour foam, 0.1–0.3 g/cm³ | Pick for buoyancy blocks, core material, packaging inserts and low-cost model stock needing some load capacity. | — | 2 | 5 | 40 Shore D |
Modelling / tooling board, 0.45–0.60 g/cm³ | Pick for styling models, master patterns and vacuum-forming tools where fast, fine-detail CNC machining is the priority. | — | 9 | — | 62 Shore D |
ISFThis page Integral-skin (self-skinning) rigid foam | Pick for one-shot mouldings that need a tough dense skin over a light core — housings, armrests, medical equipment covers. | — | 10 | 10 | 55 Shore D |
High-density / high-temperature tooling board, 0.7–1.0 g/cm³ | Pick for check fixtures, foundry patterns, vacuum-forming and low-run composite layup tools needing 90–150 °C stability. | — | 22 | — | 74 Shore D |
Rigid spray polyurea / polyurethane-urea hybrid | Pick for fast-set, seamless protective linings and abrasion coatings on tanks, decks and concrete where instant cure and toughness are needed. | — | 25 | 20 | 60 Shore D |
Mineral (CaCO₃ / alumina / talc) filled cast RPU | Pick for cost-reduced, low-shrink, high-stiffness cast tools, machine bases and thermally conductive backing masses. | — | 30 | 2 | — |
CastDefault As cast | Pick for solid cast parts, jigs, gauges, potting and machined blocks where full-density stiffness and hardness are needed. | — | 55 | 6 | 80 Shore D |
30% glass-fiber / milled-glass reinforced RIM-SRIM | Pick for stiff, dimensionally stable structural mouldings — body panels, housings, fixture plates — where CTE must be reduced. | — | 70 | 2 | — |
What is RPU ISF?
RPU ISF is RPU in the ISF grade — pick for one-shot mouldings that need a tough dense skin over a light core — housings, armrests, medical equipment covers. RPU ISF has a tensile strength of 10 MPa (1.45 ksi), weaker than 81% of polyurethane grades. Elongation at break is 10% and the elastic modulus is 0.5 GPa (0.0725 Msi). RPU ISF has a density of 0.5 g/cm³ (0.0181 lb/in³), lighter than 90% of polyurethane grades. Its glass-transition temperature is 95°C (203 °F). Cast is the default condition FabDigit quotes; ISF is available on request or by drawing note.
Advantages
- Lightweight — 0.5 g/cm³ (0.0181 lb/in³), better than 90% of polyurethane grades
- Easy to machine — 75/100, better than 83% of polyurethane grades
- Low moisture uptake — 0.3%, better than 81% of polyurethane grades
Limitations
- Low fracture toughness — 0.6 MPa·√m (0.546 ksi·√in), worse than 100% of polyurethane grades
- Poor heat conductor — 0.09 W/m·K (0.052 BTU/hr·ft·°F), worse than 90% of polyurethane grades
- High mold shrinkage — 0.6%, worse than 75% of polyurethane grades
RPU ISF properties
Typical room-temperature values for RPU ISF; 22 are specific to this condition. Other listed values are RPU reference data and may not represent this condition. Bars are the position among polyurethane grades.
Physical4
RPU ISF has a density of 0.5 g/cm³ (0.0181 lb/in³), lighter than 90% of polyurethane grades. Its glass-transition temperature is 95°C (203 °F).
Mechanical16
RPU ISF has a tensile strength of 10 MPa (1.45 ksi), weaker than 81% of polyurethane grades. Elongation at break is 10% and the elastic modulus is 0.5 GPa (0.0725 Msi).
Thermal10
RPU ISF is rated for continuous service to 80°C (176 °F). It conducts heat at 0.09 W/m·K (0.052 BTU/hr·ft·°F), worse than 90% of polyurethane grades. Thermal expansion is 80 µm/m·K (44.4 µin/in·°F).
Electrical7
RPU ISF is an electrical insulator with a dielectric strength of 18 kV/mm (457.2 V/mil) and a resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (70/100), worse than 74% of polyurethane grades. UV resistance is poor.
Sustainability4
Producing a kilogram of RPU ISF takes about 103 MJ of energy and emits 4.6 kg of CO₂ — less than 62% of polyurethane grades. Typical recycled content is 3%.
Manufacturability7
RPU ISF's machinability is very good (75/100, better than 83% of polyurethane grades); weldability not recommended (0/100); formability not recommended (10/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with RPU ISF
Is RPU easy to machine?
Machines fast and cleanly with sharp carbide or HSS tooling at high spindle speed and low feed pressure; use dust extraction and a respirator, and seal machined foam faces before painting.
Can RPU be welded?
Not weldable — thermoset; join with PU or epoxy adhesives, or cast in inserts during pour.
Can RPU be formed, bent or molded?
Two-component open pour, closed-mould casting, RIM/SRIM or spray; degas and preheat components, hold mould 40–70 °C, and demould after 20–120 min with full cure at 60–80 °C.
What surface finishes work on RPU?
Sand progressively, fill pinholes with PU putty, then prime and paint; aromatic systems need an aliphatic PU or acrylic topcoat for outdoor colour stability.
RPU 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 component; index typically 105–120 for PU, 200–350 for PIR | 40 – 60 | 50 |
| blowing agent (HFC/HFO, cyclopentane or foamed grades only; 0 for solid cast | 0 – 15 | 4 |
| silicone surfactantcell regulator | 0.5 – 2.5 | 1.5 |
| amine / tin catalyst | 0.3 – 2.5 | 1.2 |
| flame retardant (TCPP / phosphate ester)FR and B1 grades | 0 – 15 | 0 |
| mineral or glass fillerfilled/reinforced variants | 0 – 40 | 0 |
| polyether / polyester polyol (combined psucrose/sorbitol-initiated high-functionality polyol for rigid systems | ≥ 35 (balance) | — |
RPU ISF — frequently asked
What is RPU ISF used for?
RPU ISF is typically used for tooling boards, structural foam cores, rigid insulation panels and model/pattern making. In short: rigid tooling-board polyurethane; wide density and fill range; fast, clean machining.
What is the tensile strength of RPU ISF?
RPU ISF has a typical tensile strength of 10 MPa (1.45 ksi) — weaker than 81% of polyurethane grades. Strength varies by condition: see the 10 listed tempers.
Is RPU ISF easy to machine?
Yes — machinability is rated very good (75/100, better than 83% of polyurethane grades). Machines fast and cleanly with sharp carbide or HSS tooling at high spindle speed and low feed pressure; use dust extraction and a respirator, and seal machined foam faces before painting.
Can RPU ISF be welded?
Not readily — weldability is rated not recommended (0/100). Not weldable — thermoset; join with PU or epoxy adhesives, or cast in inserts during pour.
What surface finishes work on RPU ISF?
Sand progressively, fill pinholes with PU putty, then prime and paint; aromatic systems need an aliphatic PU or acrylic topcoat for outdoor colour stability.
Can RPU ISF be formed, bent or molded?
Two-component open pour, closed-mould casting, RIM/SRIM or spray; degas and preheat components, hold mould 40–70 °C, and demould after 20–120 min with full cure at 60–80 °C.
What is the maximum service temperature of RPU ISF?
RPU ISF is rated for continuous use to about 80°C (176 °F), and briefly to 130°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM D1622 / D1621 — Density and Compressive Properties of Rigid Cellular Plastics — ASTM (2020)
- EN 14315-1 — In-situ formed sprayed rigid polyurethane foam products — CEN (2013)
- Engineered Materials Handbook Vol.2 — Engineering Plastics (Polyurethanes) — ASM International (1988)
- Rigid polyurethane systems and tooling board technical data — Huntsman / Covestro / RAMPF / Sika Axson (2023)
- CES/Ashby polymer property records — rigid PU foam and cast PU — Granta Design (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.