Use this calculator to convert PU foam density between kg/m³ and lb/ft³, and to estimate how much polyurethane system you need for a given volume of foam. Enter your panel or cavity dimensions and a target density, and it returns the total system weight, the A (polyol) and B (isocyanate) split, and a drum count you can put straight into a purchase order.
A = polyol blend (white side) · B = isocyanate. This is the SPC convention and is the reverse of the North-American spray-foam habit of calling the isocyanate "A". The A:B ratio above is a placeholder — always use the exact ratio on the technical data sheet (TDS) of the system you order. Figures are an estimate for planning and purchasing; actual consumption depends on your process, mould temperature, over-pack and free-rise vs moulded density.
1 lb/ft³ = 16.0185 kg/m³. US and UK buyers usually specify foam in pcf (pounds per cubic foot); most datasheets outside North America use kg/m³.
| Common grade | kg/m³ | lb/ft³ |
|---|---|---|
| Spray, closed-cell (free rise) | ≥30 | ≥1.87 |
| Rigid panel, cyclopentane | 30–43 | 1.87–2.68 |
| Rigid panel (ES6220) | ≥40 | ≥2.50 |
| Flexible, high-resilience | 40–45 | 2.50–2.81 |
| Rigid structural / acoustic, water-blown | 80–120 | 4.99–7.49 |
How PU foam density is calculated
Foam density is simply mass divided by volume. To go the other way — from a part you need to fill to the raw material you must buy — the arithmetic is:
System weight (kg) = cavity volume (m³) × target density (kg/m³) × (1 + allowance)
The allowance covers purge, flash, mould losses and over-pack. Ten percent is a common planning figure for panel work; short shots, complex mould geometry and cold moulds push it higher. Note that moulded density is normally higher than the free-rise density printed on a datasheet, because the foam is packed into a fixed cavity.
Choosing a target density
Density is the single biggest lever on both cost and performance. Higher density buys compressive strength, dimensional stability and better surface quality; it also raises material cost roughly in proportion. Typical working ranges from our own product data sheets:
- Rigid panel foam, cyclopentane-blown — 30–43 kg/m³. Insulated sandwich panels, cold rooms, appliance cabinets.
- Rigid structural / acoustic foam, water-blown — 80–120 kg/m³. Structural panels and sound-insulating panels where load-bearing matters more than lambda.
- Flexible high-resilience foam — 40–45 kg/m³. Furniture and seating.
- Closed-cell spray foam — free rise from 30 kg/m³. On-site insulation and waterproofing.
If you are unsure which band your application sits in, send us the part and the performance target rather than a density — we will work the density back from the requirement.
A and B components — get the naming right
Throughout our documentation, A is the polyol blend (the white side) and B is the isocyanate. This is the convention used across our technical data sheets and drum labels. Be aware that much of the North-American spray-foam industry uses the opposite habit, calling the isocyanate the “A side”. When you place an order or read a mixing ratio, always confirm which component the letter refers to.
The A:B ratio in the calculator is a placeholder for planning only. Every system has its own ratio — take it from the technical data sheet for the exact grade you buy.
FAQ
How do I convert kg/m³ to lb/ft³?
Divide by 16.0185. For example 35 kg/m³ is 2.19 lb/ft³. Buyers in the United States and the United Kingdom usually specify foam in pcf (pounds per cubic foot), while datasheets elsewhere use kg/m³, so the two figures often need reconciling on the same order.
Is free-rise density the same as the density in my part?
No. Free-rise density is measured with the foam expanding unrestricted, which is what most datasheets quote. Foam injected into a closed cavity is packed to a higher moulded density, commonly 10–20 percent above free rise, in order to fill corners and achieve a sound surface. Size your purchase on the moulded density you actually run.
Does higher density always mean better insulation?
No. Thermal conductivity for rigid PU passes through an optimum: below it the cell structure is too coarse and open, above it you are simply adding polymer mass that conducts heat. Raising density well past the optimum buys compressive strength and dimensional stability, not a lower lambda.
How much material do I need for one cubic metre of foam?
The system weight equals the volume multiplied by the target density, plus an allowance for waste. One cubic metre at 35 kg/m³ needs about 35 kg of system, or roughly 39 kg once a 10 percent allowance is included, split between the A and B components according to the ratio on the datasheet.
What is the minimum order quantity?
Ask us with your calculated tonnage — MOQ and lead time depend on the grade and the destination. Use the quote button in the calculator and the quantity is carried across automatically.
