Thermal Bridging

The purpose of insulation is to slow down the movement of heat, and most of that effect occurs by slowing conductive heat transfer. The higher the conductivity of a material, the more quickly heat can move through it. Insulation materials are rated by their resistance to heat transfer, a term we call R-value. The higher the R-value, the lower the heat transfer.

When different materials with different thermal conductivities span from the warm side to the cold side of an assembly, more heat flow occurs through the material with higher conductivity. If the differences are large enough, that heat flow essentially short-circuits the insulation—a process referred to as thermal bridging.