The measure of a material s ability to insulate is called its R-value. The greater the R-value, the greater the resistance to conduct heat flow. In modern construction, insulation is used to form a barrier to heat flow. This barrier completely surrounds conditioned spaces to protect them from outdoor influences. No insulation, regardless of its R-value, can totally stop heat flow.
All structures have gaps or weak spots such as doors and windows.
R-value can be diminished or lost if the insulating material is compressed or compacted. Care should be exercised to match the insulation material to the area to be insulated. Avoid compacting to assure proper R-value. Batts and blankets are easily installed during construction, but are difficult to retrofit to finished structures. These are usually foam boards made from Polystyrene or urethane.