Lambdavärden

Lambdavärden, often referred to as lambda values, represent the thermal conductivity of a material in building physics. Specifically, it quantifies how effectively a material conducts heat. A low lambdavärde indicates that the material is a good insulator, meaning it resists the flow of heat. Conversely, a high lambdavärde signifies that the material is a poor insulator and conducts heat readily.

The unit for lambdavärde is watts per meter-kelvin (W/(m·K)). This unit reflects the amount of heat energy (in watts) that will transfer through a one-meter thick layer of the material, across a one-square-meter area, when there is a one-kelvin temperature difference across that layer.

In construction and insulation, materials with low lambdavärden are preferred for building envelopes to minimize heat loss in winter and heat gain in summer. This contributes to improved energy efficiency and thermal comfort within buildings. Common insulating materials like mineral wool, polystyrene foam, and polyurethane foam have low lambdavärden. Materials like concrete and steel, on the other hand, have significantly higher lambdavärden and are therefore poor insulators.

The lambdavärde is an intrinsic property of the material itself, independent of its thickness. However, when considering the overall insulating performance of a component, such as a wall or roof, the U-value (or värmegenomgångskoefficient) is used. The U-value takes into account the thickness and the lambdavärde of all the materials in the component, as well as any air gaps or surface resistances, to determine the total heat transfer.