Definition
Open-cell spray foam
A soft, low-density variety of polyurethane spray foam insulation. Around 0.5 lb/cu ft density. Easier and cheaper to remove than closed-cell.
Open-cell spray foam expands rapidly when sprayed, creating a soft, flexible foam with interconnected air pockets.
It's lighter, less expensive to install, and provides moderate thermal performance.
In the UK loft retrofit context — particularly under ECO4 grants — it was widely chosen because it qualified for the grant and could be applied quickly.
Mortgage lenders refuse properties with either open-cell or closed-cell foam in the roof void; removal is required either way.
Open-cell removal is faster and runs £50-60 per m² in West Yorkshire.