Block fill foam insulation refers to an insulating material injected into hollow block and hollow cavity walls. The foam is injected under pressure with the wall which forces itself into adjacent columns, cracks, and crevices. After the block or brick wall is insulated it forms a protective envelope around the building preventing air leaks, sound transmission, mold/mildew/bacteria, and seals out pollutants and allergens. The foam is injected through a drilled hole in the masonry wall and typically sets up in 10-60 seconds.