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Open and closed cell foam are two different types of spray foam insulation. They have different strengths and weaknesses, and one is not necessarily better than the other. It comes down to understanding the benefits of open cell vs closed cell foam and choosing the type that fits your needs.

A spray insulation is referred to open cell or closed cell because of the difference between the small bubbles (cells) that make up the foam. Open cell foam is full of cells that are not completely encapsulated. In other words, the cells are deliberatly left open. This makes the foam a softer, more flexable material. Closed cell foam is made up of cells that are, as the name suggests, completely closed. The cells are pressed together, so air and mositure are unable to get inside the foam. Because of this, closed cell foam is much more rigid and stable than open cell foam.

Closed cell foam is much denser than open cell foam. Most open cell foam has a density of about .5 pounds per cubic foot. Closed cell foam can be over three times that, with a density of 1.75 pounds per cubic foot or more.

A foams R-value is its resistance to heat flow or, in other words, how well they insulate. Closed cell foam has a higher R-value than open cell foam, usually about 6.0 per inch. But some closed cell foams, like ISO AULIS Closed Cell formula, have even higher ratings per inch. This higher rating makes closed cell foam better at keeping heat in or out of a structure. Open cell foams have an R-value of around 3.5 per inch. This is significantly lower than closed cell foams, which can limit open cell insulations usefulness in extreme temperature conditions.

This is one of the most important differences from an application standpoint. Closed cell foam is designed to expand to about 1" of thickness when sprayed. With each inch offering an r-value of 7, multiple applications can be applied to achieve higher total r-values. Open cell foam is designed to expand to 3" of thickness, meaning only one application is possible in most standard walls.

What Do All These Terms and Ratings Actually Mean? At this point, you might be still be trying to decipher which type of foam insulation is right for your project. Here is a quick summary of open cell vs closed cell foam strengths and the best applications for each: Benefits of Closed Cell Foam Closed cell foam is the best choice for robust insulating where space is an issue, as it can achieve 2x the R-Value of open cell inside a standard wall. Its rigid nature also adds to the structural integrity of the building and E84 fire rated versions are available. The closed cell also acts as a vapor barrier, so water and moisture will be less likely to get inside the home, and the foam itself is unharmed by water damage. Benefits of Open Cell Foam One of the biggest benefits of open cell foam is that it expands so much after it has been applied, meaning it can insulate hard to reach nooks and crannies in a home. These types of areas can be hard to insulate with closed cell foam. Open cell foam is excellent for soundproofing where a single application can completly fill the area between studs. Open cell foam is also much more affordable than closed cell foam, however this foam wont insulate a house as well as closed cell foam, so it is not ideal for locations with extreme weather temperatures. We recommend closed cell for the best thermal protection as open cells are mostly just a filling material.