Open vs Closed
Cell Foam Insulation
What is the difference between open and closed cell foam
Spray Foam is categorized into two types, "open-cell" or
"closed-cell”. Open cell is lightweight foam that is flexible,
and an excellent air barrier. Open cell foams most commonly
range from .5 lb to .7lb densities. Closed cell foam is higher
density foam, and a moisture barrier. Most closed cell foam
used for insulation range from 1.7 lb to 2 lb. Closed cell
foam can go up to 3 lb density which is often used in exterior
roof applications (like the Superdome).
The main differences between open and closed cell foam are
moisture permeability, R-Value, and flexibility. Closed cell
foam is a moisture vapor barrier. What this means is that it
will not allow moisture to pass through the foam. Open cell
foam is not a moisture vapor barrier, and will allow moisture
to pass. Closed cell has a higher R-value than open cell.
R-value should not be the determining factor when it comes to
spray foam see R value versus Performance value. Closed cell
foam is around, 6.6 per inch as compared to 3.8 per inch in
open cell. However, both foams are air barriers, and it is the
air barrier that makes foam such an excellent insulation.
Closed cell foam is much more expensive than open cell foam.
Closed cell foam is more rigid.
So which foam is best? The best foam to use should be
determined by the application. Some spray foam contractors
recommend closed cell foam in some applications since their
open cell foam tends to absorb moisture. All foams are not
created equal. In some applications, open cell foam with a
vapor retarding paint is the best application.
Closed cell foam should never be used on wooden roof decks.
Moisture will be trapped in the roof's wood decking if you
were to apply closed cell foam to the underside of the roof of
a home and the roof develops a leak. This can lead to rotting
of the roof deck before the roof leak is ever discovered. Open
cell foam is not a vapor barrier, so it allows the water from
the roof leak to weep through the foam to the space below so
it is the better choice for most residential applications.
In most applications, the buildings energy performance will be
the same regardless whether you used open or closed cell foam.
Open cell foam is more flexible than closed cell foam. When
the framing members expand and contract with the weather, or
are impacted by high winds, open cell foam will flex with the
structure. Closed cell foam however, will not flex, a will get
hairline cracks where it was connected to the studs and walls
and lose some of its benefits.
Open cell foam is usually more suitable for residential
applications because of its moisture permeability, or the
ability for moisture to pass through the insulation. (See
above) Most homes are constructed out of wood, and it is this
reason, moisture permeability, that is the main reason why
open cell foam is best suited for your home.
Closed cell foam is best used in refrigeration, marine,
industrial, and roofing or, when we are trying to solve a
moisture problem and the problem can't be solved with a vapor
retardant paint. Closed cell foam is commonly found outdoors.