• Similar to the debate between fiberglass and cellulose, foam manufacturers products also have their differences.
• Three general requirements must be met by foam products in applications where they replace fiberglass.

1. Foam must meet a perm rating acceptable to the application.  Typically a perm rating of 1.  This is the point at which the material is considered a vapor barrier and would replace the application of poly.
2. Foam must meet a specific flame spread or be resistant to burning.  When replacing fiberglass which is very resistant to fire, foam applications must be looked at carefully because of their flammable characteristics.
3. Foam must then beet the insulating requirement for the particular application.  This is where the product tends to exceed traditional fiberglass applications.  The R-value per inch of foam is higher than virtually all fiberglass materials and cellulose.

So why isn't foam used in every house?

Pro and Con

• Foam costs are generally 2.5 to 3 times as much as the same fiberglass applications.  That is for the same OR-value.  If you want to take advantage of the higher insulating value then it can get more expensive from there. 
• The closed cell polyurethane spray foam does have a sustained R-Value between 6 to 7 per inch depending on the manufacturer.

1. Insulation is a relatively small percentage of the total cost of a new home.  The greater OR-value and stability characteristics can easily outweigh the small total increase in the price of a new home.  In an average 2x6 frame wall a fiberglass batt will achieve an R-19 to 22, Foam can achieve an R-33 to 37. 

• Between 2 to 3 inches it becomes an acceptable vapor barrier for general building purposes.

1. This quality of foam makes it a wonderful application in where the traditional poly vapor barrier is difficult if not impossible to install.  One such area being the rims between floors.  With closed cell polyurethane foam the rims can be both insulated and sealed well.  The rim are makes up such a small percent of the wall area in a house that the increased price of the product becomes negligible.