Spray foam or foam-in-place insulation can be sprayed into walls, on attic surfaces, or under floors to insulate and reduce air leakage. There are two types of foam-in-place insulation: closed-cell and open-cell. Both are typically made with polyurethane. Closed-cell foam has a greater insulation value and provides stronger resistance against moisture and air leakage. Open-cell foam is lighter and less expensive but should not be used below ground level where it could absorb water.