Spray foam comes in two main types, open cell and closed cell. They look similar going on, but they behave very differently once they cure, and using the wrong one in the wrong place wastes money. Here is how to tell which one belongs in your house or building.
The quick comparison
| Open cell | Closed cell | |
|---|---|---|
| Texture | Soft, spongy | Hard, rigid |
| R-value per inch | About R-3.5 to R-3.8 | About R-6 to R-7 |
| Moisture | Vapor open | Vapor retarder |
| Sound control | Better | Less |
| Installed price | Lower | Higher |
A board foot, the unit spray foam is priced in, is one square foot at one inch thick.
What open cell foam is good at
Open cell foam expands a lot as it is sprayed, filling big cavities quickly and cheaply. The cells are not fully closed, so the cured foam is soft and lets water vapor pass through.
- Attic roof decks. This is the most common use in Central Texas homes. Foam on the underside of the roof deck seals the attic and brings the air handler and ducts inside the conditioned space.
- Interior walls and floors. It is good at softening sound between rooms.
- Big, open areas where you want air sealing and solid R-value without paying for closed cell.
What closed cell foam is good at
Closed cell foam is dense and rigid. It packs nearly twice the R-value per inch and acts as a vapor retarder, which is exactly what you want in some places.
- Metal buildings, shops and barns. It bonds to the metal and stops condensation. See how to stop condensation in a metal building.
- Crawl spaces and rim joists, where moisture is a concern.
- Tight spaces where you need the most R-value in the least depth.
Which one for your project?
- Hot attic with ductwork in a home: usually open cell on the roof deck.
- Metal shop or barn: closed cell.
- Crawl space or rim joist: closed cell.
- Interior walls for sound: open cell or batts.
- Attic only needs more depth: neither. Blown in insulation is usually the better value.
A note on installation
Either foam is only as good as the install. It has to go on at the right thickness, in the right conditions, with coatings where local code requires them, and the house has to be vacated for the re-entry time the manufacturer specifies. Ask any installer which product they use, how thick they will spray it and what is included.
Want a recommendation for your house? We will inspect it for free and put it in writing. Learn more about spray foam insulation in Bell County.