Thermal conductivity () or Lambda value is expressend inW/mK.It is the heat flow in Watts/m² for a temperature gradient of 1K per metre thickness.

The lower the value, the better the insulation.Thermal resistance (R) expressed in

m²K/Wis the measure of resistance to the passage of heat for a given thicknesst.R = t/

The higher the R-value, the better the insulation

U-value (or K-value) expressed as W/m²K is the coefficient of thermal transmittance and is the reciprocal thermal resistance R so: U = 1/R

This is the amount of energy passing through a material or structure in one hour expressed in Watts per Metre² for a temperature difference between the two surfaces of 1C (=1 Kelvin).

Hence, the lower the U-value, the better the insulation.

The U-value of a system or structure is the reciprocal of the total thermal resistance value of each component element of the structure:

i.e. U = 1/R1 + R2 + R3 ... etc.

NOTE: since R = t () and U = 1/R

U = 1/t/( l ) which = 1 X ( l )

so

U = ( )/t therefore when t = 1 metre, U = value.Please test our U-Value Calculator

continue to Builders - Thermal Conductivity