Insulation: Open v. Closed Cell Foam
Photo: SPF being applied.
Spray Polyurethane Foam (SPF) is available in two distinctly different types. When choosing foam for your project you must choose the right type for the right application. Please note: serious moisture problems can occur if the wrong type is selected for your application, this post is to serve as an introduction to foam types for our clients and potential clients. I will also include some resources at the end should you want to learn more, but please consult your builder prior to deciding what is best for you.
Moisture
Open cell: will absorb moisture, and will allow vapor to pass but not bulk air.
Closed cell: will not absorb moisture. Considered a vapor barrier.
R-Value
Open cell: approximately R3.5 per inch of foam.
Closed cell: approximately R6-7 per inch of foam.
Structure
Open Cell: weighs about .5LB per cubic foot, easily deforms when push on with a bare hand.
Closed Cell: weighs about 2LB (4x that of open cell) per cubic foot. Is extremely hard to the touch, and technically will add structural rigidity to anything you apply it to, although we don’t recommend having your design rely and added strength you obtain from foam.
Applications
Roofline: open cell SPF is an option in warm climate accompanied by proper attic ventilation to maintain appropriate humidity levels. If you are unable to condition the attic space, closed cell would be your only option.
Walls (interior): open cell is generally used here as its cheaper than closed cell. A 2x6 wall will get you about R19, same as fiberglass. We dont see the benefits here, as we get our tight air sealing from other methods. There are other insulation options for walls we like better.
Foundation walls and under slab: closed cell is the only option here as it will not absorb the moisture it may be exposed to from the concrete or soil.
Resources: