Guide
Foam density guide
On this page (10)
- What do the foam numbers mean?
- Is higher-density foam firmer?
- What density should seat cushion foam be?
- Why does density matter over time?
- What is polymer density?
- How is foam firmness measured?
- What density is memory foam?
- How do I convert lb/ft³ to kg/m³?
- What should I ask a cushion maker about foam?
- Which foam guide should I read next?
Foam density is the mass of foam per unit volume, stated in pounds per cubic foot (lb/ft³) or kilograms per cubic metre (kg/m³). Density tells you how well foam keeps its shape and support over time, not how firm it feels: the Polyurethane Foam Association (PFA) states that firmness is independent of density.
Foamera makes made-to-measure foam cushions and sells them online through TURKEX LLC. This guide explains the foam numbers you see when you compare cushions; the fill choices on Foamera product pages are on the foam and fill page.
What do the foam numbers mean?
Density, firmness and support factor are separate measurements, so ask for all three when you compare foams.
| Property | What it measures | Unit | Range given by PFA |
|---|---|---|---|
| Density | Mass per unit volume | lb/ft³ or kg/m³ (1 lb/ft³ ≈ 16.02 kg/m³) | Flexible polyurethane foam: about 0.5–6 lb/ft³ (8–96 kg/m³) |
| Firmness (IFD) | Force needed to indent a sample by 25% of its height | Pounds of force | No single range; ask the maker for the figure |
| Support factor | 65% IFD divided by 25% IFD | Ratio | About 1.5–2.6; 2.0 or above suits seat cushions |
| Resilience | Surface springiness, measured by ball rebound | Percent | About 20–80% |
| Compression set | Permanent loss of height after compression | Percent of original height | Decreases as density goes up |
Is higher-density foam firmer?
No. PFA states that firmness is independent of foam density, and that high-density foam can be made very soft. Density relates to durability and support, while firmness (IFD) describes how the surface feels.
What density should seat cushion foam be?
PFA cites industry research that polyurethane foams with a polymer density of 1.8 lb/ft³ (29 kg/m³) or higher perform better in seating than lower-density foams. The same PFA case study reports that many furniture makers and retailers now encourage buyers to look for seat foam of 1.8 lb/ft³ (29 kg/m³) or higher.
Support matters as well: PFA notes that foams with a support factor of 2.0 or above are better suited to load-bearing uses such as furniture seat cushions.
Why does density matter over time?
Higher-density foam generally keeps its original properties longer. PFA reports that firmness loss after repeated flexing is usually smaller as polymer density increases, and that height loss (compression set) decreases as density goes up.
What is polymer density?
Polymer density is the density of the foam chemistry alone, without additives or fillers. When additives or fillers are used, the overall foam density is higher than the polymer density, so PFA advises using the polymer density when you specify foam.
How is foam firmness measured?
Firmness (IFD, indentation force deflection) is usually measured as the force in pounds needed to press a 50 in² (323 cm²) circular indentor foot into a 4 in (10 cm) thick sample, typically 15 in (38 cm) square or larger, to a set percentage of its height. The figure at 25% describes surface feel, and some guides write ILD for the same kind of firmness figure.
What density is memory foam?
Memory (viscoelastic) foam in household and healthcare products typically ranges from 2 to 6 lb/ft³ (32 to 96 kg/m³), according to PFA. Memory foam recovers slowly after compression and becomes firmer in cold conditions. Memory foam is not one of the fill choices on Foamera product pages; see HD foam vs memory foam.
How do I convert lb/ft³ to kg/m³?
Multiply lb/ft³ by 16.02 to get kg/m³, or divide kg/m³ by 16.02 to get lb/ft³.
| lb/ft³ | kg/m³ |
|---|---|
| 1.5 | 24 |
| 1.8 | 29 |
| 2.0 | 32 |
| 2.5 | 40 |
| 3.0 | 48 |
What should I ask a cushion maker about foam?
- The density in lb/ft³ or kg/m³, and whether it is the polymer density.
- The firmness (25% IFD) and the support factor.
- Whether a fiber wrap is added: PFA notes that seat cushions are often wrapped with polyester or cotton batting to soften the surface.
On Foamera product pages you choose High Density Foam, Fiber Fill or Cover Only, and you can add a Fiber Wrap as an extra. Start with bench cushions, chair cushions or sofa and couch cushions, or go straight to the bench cushion or the window seat and nook cushion.
Which foam guide should I read next?
- Best foam for seat cushions
- Best foam for couch cushions
- HD foam vs memory foam
- How to fix sagging couch cushions
- Best foam for outdoor cushions
- What is dry-fast foam?
- How long do outdoor cushions last?
- What foam and fill Foamera uses
- What goes into a Foamera cushion
Sources
- Polyurethane Foam Association, Foam Performance, Glossary and Furniture Case Study. Accessed 26 September 2026.
- Polyurethane Foam Association, IN•TOUCH Vol. 1 No. 2, The Importance of Density (revised 2016). Accessed 26 September 2026.
- Polyurethane Foam Association, IN•TOUCH Vol. 11 No. 1, Viscoelastic (Memory) Foam (revised 2016). Accessed 26 September 2026.
- Unit conversion: 1 lb/ft³ = 16.02 kg/m³ and 1 in = 2.54 cm, from the exact definitions of the pound and the foot (NIST).