Concepts » 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