Light density open cell spray foam insulation and medium density closed cell spray foam insulation.
Open or closed cell foam for attic.
The myth that open cell is more economical is bullshit.
There you have it.
Closed cell foam is much denser than open cell foam.
While the denser closed cell variety does not readily absorb moisture open cell foam can draw it in like a sponge.
Most open cell foam has a density of about 5 pounds per cubic foot.
Do it right and your roof will not rot.
I have open cell in my house since 2004 and i would not use it in a dogs out house.
These two types of spray foam insulation both contain polyurethane that can be potentially dangerous to the environment and to health upon exposure.
There is 300 difference there but the cost they give you is about a third difference and open cell foam at 12 inches will not give you the performance of 2 inches of closed.
This type of spray polyurethane foam can be classified into two different types.
Using spray foam insulation in an unvented attic application.
Others like david butler see his comment below say you need to do it only if a moisture problem develops.
Open cell should be at least 6 inches in depth and closed cell 4 inches or more of each depending on local code.
Lstiburek says to do it for every spray foam attic.
Open cell foam weighs 1 2 pound per cubic foot and closed cell weighs 2 lbs per cubic foot.
A foams r value is its resistance to heat flow or in other words how well they insulate.
Open cell spray foam is a perfectly acceptable insulation product to use in attics.
Open cell foam has an r value of about 3 5 to 3 7 per inch while closed cell foam has an r value of about 6 per inch.
Both low density open cell and medium density closed cell spray foam can be used in an unvented attic to provide the needed thermal resistance and airtightness.
Closed cell foam can be over three times that with a density of 1 75 pounds per cubic foot or more.