The Greek letter λ, lambda, [W/mK] is used to represent the heat conductivity of a material. The heat conductivity of a material is thus popularly known as its lambda value. The lambda value is used for thermal calculations on buildings and thermal components (insulation, etc.).

Lambda value λ (w/mK) is a measure of the rate at which heat passes through a material. The units are watts per unit thickness per degree temperature difference across that unit thickness. Examples include Glass mineral wool Loft roll at 0.044w/mk, and Celotex GA4000 PIR board at 0.022w/mk.

The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction.

It is also called the lambda (λ) value, or k value. A material’s thermal conductivity is the number of Watts conducted per metre thickness of the material, per degree of temperature difference between one side and the other (W/mK).

The lambda value, also portrayed as ‘K-value’ or ‘λ-value’, measures a product’s thermal conductivity in units of W/mK. Good insulation will have as low a lambda value as possible to reduce heat loss. For example, our lower lambda products each have a lambda value of 0.019 W/mK across all thicknesses.