A unit of measure of thermal resistance. The higher the value, the better the heat-insulating capabilities of the material. For example, an 8” lightweight concrete block has an R-Value of 2.00 and a 1/2” sheet of plywood has an R-Value of .63. The concrete block has far better heat-insulating properties than the plywood. This unit is used to find the ‘heat-loss calculation’ for a home so that preparations can be made to properly heat a home. Radiant heating systems need low R-Values for carpet pads to allow the heat to pass through it and high R-Values are encouraged everywhere else.