Open-cell spray foam density is approximately

• A. 2 lb/ft³
• B. 1.5 lb/ft³
• C. 0.5 lb/ft³
• D. 5 lb/ft³

Answer: (C)

Open-cell spray foam is a lightweight, airy foam because its cells are mostly open and interconnected, containing a lot of air. That structure gives it a low bulk density, typically around 0.5 pounds per cubic foot. Density here is a measure of how much material fills a given volume, and the open, cell-rich makeup means much less material per cubic foot compared to other foams, which is why it’s about 0.5 lb/ft³.

In contrast, closed-cell spray foam has much higher density—around 2 lb/ft³—because its cells are sealed and filled, making it stiffer and providing more insulation per inch. Numbers like 1.5 lb/ft³ are not typical for standard open-cell foam, and 5 lb/ft³ would be far too dense for ordinary spray foams. So the familiar open-cell density sits at approximately 0.5 lb/ft³.