Sofa Foam Density Explained: What 28kg/m3 vs 35kg/m3 Means for Comfort & Lifespan

Foam density measures mass rather than firmness, and our 2026 analysis finds that this single confusion causes most disappointment with sofa comfort. A cushion at 35kg/m3 contains around a quarter more polyurethane per cubic metre than one at 28kg/m3, which determines how long it resists compression set, while hardness is tested separately and determines how the seat feels on the first day. High density soft foam exists, but product pages rarely explain the combination. Furniture in Fashion sets out why denser foam distributes each compression across more cell walls and therefore deforms permanently more slowly, why back cushions are correctly specified softer than seats, and why a dropped seat is often a suspension failure rather than a foam failure. The report also covers the dimensions that no specification can compensate for: seat depth of 55cm to 60cm for upright sitting, and a finished seat height of 45cm to 48cm for easy standing....