RPU
RPU is a rigid, cross-linked polyurethane cast or foamed for structural foams, tooling boards, patterns and insulation, with conditions covering solid cast, 40 and 200 kg/m³ foams, 0.5 and 0.8 tooling boards, GF30, mineral-filled, flame-retardant, polyurea and integral-skin variants.
Reference datasheet — RPU 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.
Values for the Cast condition
RPU grades and fills
RPU is supplied in 10 conditions, soft to hard. Cast is the default FabDigit quotes; the values on this page are for it.
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 | ||
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?
RPU is a rigid, cross-linked polyurethane cast or foamed for structural foams, tooling boards, patterns and insulation, with conditions covering solid cast, 40 and 200 kg/m³ foams, 0.5 and 0.8 tooling boards, GF30, mineral-filled, flame-retardant, polyurea and integral-skin variants. The solid default at 1.15 g/cm³ gives 55 MPa tensile strength, 6 % elongation, Shore D 80, 0.21 W/m·K and service to 85 °C, with good stiffness-to-weight and dimensional stability for models and jigs. It is a thermoset — not weldable — and the 85 °C limit plus aromatic yellowing restrict hot or outdoor service. Epoxy tooling board is the usual alternative where higher temperature resistance is needed. RPU has a density of 1.15 g/cm³ (0.0415 lb/in³), heavier than 62% of polyurethane grades. Its glass-transition temperature is 95°C (203 °F). RPU has a tensile strength of 55 MPa (7.98 ksi), stronger than 64% of polyurethane grades. Elongation at break is 6% and the elastic modulus is 2.4 GPa (0.348 Msi).
What is RPU used for?
- Tooling boards
- Structural foam cores
- Rigid insulation panels
- Model/pattern making
Advantages
- Easy to machine — 85/100, better than 95% of polyurethane grades
- Low moisture uptake — 0.3%, better than 81% of polyurethane grades
Limitations
- Low fracture toughness — 1.3 MPa·√m (1.18 ksi·√in), worse than 90% of polyurethane grades
- Limited ductility — 6%, worse than 83% of polyurethane grades
- High mold shrinkage — 0.9%, worse than 83% of polyurethane grades
RPU properties
Typical room-temperature values for RPU-Cast; bars are the position among polyurethane grades.
Physical4
RPU has a density of 1.15 g/cm³ (0.0415 lb/in³), heavier than 62% of polyurethane grades. Its glass-transition temperature is 95°C (203 °F).
Mechanical16
RPU has a tensile strength of 55 MPa (7.98 ksi), stronger than 64% of polyurethane grades. Elongation at break is 6% and the elastic modulus is 2.4 GPa (0.348 Msi).
Thermal10
RPU is rated for continuous service to 85°C (185 °F). It conducts heat at 0.21 W/m·K (0.121 BTU/hr·ft·°F), better than 74% of polyurethane grades. Thermal expansion is 80 µm/m·K (44.4 µin/in·°F).
Electrical7
RPU 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 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's machinability is excellent (85/100, better than 95% of polyurethane grades); weldability not recommended (5/100); formability not recommended (5/100).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the polyurethane family
Yield strength against density for every polyurethane grade FabDigit runs. RPU is highlighted; hover a dot for its name, or open the interactive family chart.
Working with RPU
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.
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) |
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.
How much does RPU cost?
RPU is a standard-cost polyurethane ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
RPU — frequently asked
What is RPU used for?
RPU is typically used for tooling boards, structural foam cores, rigid insulation panels and model/pattern making. In short: rigid tooling-board polyurethane; wide density and fill range; fast, clean machining.
What is the tensile strength of RPU?
RPU has a typical tensile strength of 55 MPa (7.98 ksi) — stronger than 64% of polyurethane grades. Strength varies by condition: see the 10 listed tempers.
Is RPU easy to machine?
Yes — machinability is rated excellent (85/100, better than 95% of polyurethane grades). Machines fast and cleanly with sharp carbide or HSS tooling at high spindle speed and low feed pressure; use dust extraction and a respirator, and seal machined foam faces before painting.
Can RPU be welded?
Not readily — weldability is rated not recommended (5/100). Not weldable — thermoset; join with PU or epoxy adhesives, or cast in inserts during pour.
What surface finishes work on RPU?
Sand progressively, fill pinholes with PU putty, then prime and paint; aromatic systems need an aliphatic PU or acrylic topcoat for outdoor colour stability.
Can RPU be formed, bent or molded?
Two-component open pour, closed-mould casting, RIM/SRIM or spray; degas and preheat components, hold mould 40–70 °C, and demould after 20–120 min with full cure at 60–80 °C.
What is the maximum service temperature of RPU?
RPU is rated for continuous use to about 85°C (185 °F), and briefly to 130°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does RPU cost?
RPU is a standard-cost polyurethane ($$), cheaper than about 71% 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 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; 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.