Foam-iT! rigid foams are closed cell. Closed cell foams provide a better surface finish, especially when backpressure is applied during casting. Closed cell foams also provide better water resistance. Flex Foam-iT! flexible foams are "hybrid" foams, they combine characteristics of both closed-cell and open-cell foams with a mixture of closed and open cells within the matrix. Even though Flex Foam-iT! foams have some open cells, they do not fully absorb water when cured.