Knowledge Center: Closed Cell vs Open Cell Foams
Dense foams have what’s known as a closed-cell structure, which means that the gas bubbles that form during the application process remain permanently locked into the cured foam. The result is something like a three-dimensional bubble wrap with extremely tiny bubbles. Because there are no interconnections between individual bubbles, the foam absorbs little water and also resists the passage of water vapor. According to most building codes, a vapor retarder must have a perm rating of less than 1.0 and some foams meet this standard.
Low-density open-cell foams, on the other hand, have a structure more like a very fine-grained sponge. The cured material consists of a series of tiny interconnected passageways. These open cells are too small to permit the passage of much air, but they are more permeable to water vapor than closed-cell foams.