Thermal insulation for building applications is traditionally rated on its steady-state thermal resistance, or R-value, which is the ratio of thickness to thermal conductivity. Materials with the same thermal resistance will have the same steady-state thermal performance. However the transient thermal performance of each material can be quite different due to absorption effects.

Test facilities set up by the Energy Research and Development Corporation, Wool Research and Development Corporation and CSIRO in Australia have determined that maximum daytime temperatures 29°C) can be reduced by 3°C and minimum night-time temperatures can be increased by 2°C for wool over man-made fibres. Overall efficiencies of 17.4% were recorded for wool where no vapour barrier existed.