What is the difference between U-value and λ-value?
The λ-value is the coefficient of thermal conductivity of material. It is an inherent physical property of that material and is a measure of the material’s ability to conduct heat. The U-value, or thermal transmittance, is a measure of the rate of heat flow through a complete floor, wall or roof element (which may contain many layers of different materials with different λ-values).
