Open Cell vs Closed Cell Foam: Which Should I Choose?

Open cell spray foam is also described as a “low density” or “0.5 lb.” foam, meaning if you cut a piece of open cell foam into one cubic foot (12”x12”x12”), that piece of foam would weigh approximately half of one pound. The microscopic cells within open cell foam are just that—open— which give it a soft, fluffy feeling. We often compare the texture of open cell foam to a sponge or even angel food cake. 

Generally speaking, open cell foam is better suited for residential applications— specifically above grade in exterior walls, roof lines, attic floors, and areas that need soundproofing. 

Open cell spray foam is not a moisture vapor barrier, and will allow moisture to pass. So, if you’re considering spraying foam to the roof deck of your new or existing home, you want open cell. If there’s a roof leak, water will pass through the foam, and you will quickly be able to find your problem. 

At a minimum of 3.5”, most open cell foams are considered air impermeable. Because open cell foam expands at about 100x its liquid state, every crack and crevice is filled creating a very airtight environment, and that’s really what you’re after in applying spray foam. 

Closed cell spray foam, on the other hand, is also called “medium density” or “2.0 lb.” foam. Can you guess how much one cubic foot of closed cell foam weighs? The tiny cells of medium density, 2 lb. foam are closed, and the texture is very firm and rigid. After it has cured, closed cell foam is essentially a very hard plastic. 

Closed cell spray foam is an incredible product below grade in your basement or crawl space because of its ability to block moisture.  You’ll also see closed cell used in commercial and industrial projects, pole barns, metal buildings, and exterior applications. 

At a thickness of 1.5”, many closed cell products can provide a moisture barrier to reject bulk water, and its these vapor permeability characteristics that make closed cell products perfect for insulating basement and crawl space walls. It will completely lock out the damp, musty, humid smells most basements have to fight. 

Closed cell foam expands roughly 40x its liquid state.  It is considered air impermeable at about 1.5” thick.