Concepts » Glossary

Glossary

Lambda or Thermal Conductivity value

Defines a materials ability to transmit heat. The Lambda is a given figure, there is a table of Lambda values in the building regulations part L.

Every material has its own Lambda value. The lower the figure the better the performance.

Unit of Measurement

W/mK

R-Value = Thermal Resistance

Defines a materials ability to resist heat flow. The higher the figure the better the performance.

Unit of Measurement
m2K/W

To calculate the R-Value:

Find the Lambda value (table in the building regulations, part L or on the packaging of the material).


U-Value

Defines the ability of an element of a structure to transmit heat under steady state conditions. The lower the figure the better the performance.

Unit of Measurement
W/m2

To calculate the U-Value:

Divide 1 by the R-Value

Example:

100mm Polyflat
1 / 4.348 = 0.22
U-Value = 0.22