Insulation materials are used in roofs, walls and air conditioning. They work by resisting heat flow, measured by an R-value (the higher the R-value, the greater the insulation). This R-value varies according to material type, density and thickness, and is affected by thermal bridging, unwanted heat flow that occurs at joists, studs and rafter beams. Insulation materials include aluminum foil tape, insulation sheet, insulation tape.