The rigid insulation is a foam polystyrene material that comes in various thickness to add to the current R-value of the fiberglass insulation between the rafters. One of the most common thicknesses of rigid foam insulation is 3/4 inches.

Rigid foam panels come in a variety of thicknesses and widths, but 2-ft. x 8-ft. and 4-ft. x 8-ft.

This product typically has an R value of 3.6 to 4.0 per inch of thickness.

A wall utilizing STYROFOAM T-MASS Technology with a 2-inch exterior layer and a 4-inch interior layer of concrete along with a 2-inch layer of STYROFOAM extruded polystyrene insulation would result in a material R-value of approximately 11.33.

Choose the right type of rigid foam for your needs. When choosing rigid foam insulation, you have three main options: Polyisocyanurate: Known as polyiso for short, polyisocyanurate foam has the highest R-value per inch (R-6.5 to R-6.8) of any rigid insulation.

Foam Board Insulation R-Value. Rigid foam insulation R-values range from R-4 to R-6.5 per inch of thickness, which is greater than many other insulating materials of the same thickness.

The right material for basements is rigid foam Rigid foam insulation consists of boards made of solid foam insulation and covered on one side with a radiant barrier. Rigid foam boards are attached to basement walls to seal and insulate the space. Rigid foam is ideal for the basement environment because of its water resistance and durability.