## Technical Terms Thermal conductivity () or Lambda value is expressend in *W/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/W* is the measure of resistance to the passage of heat for a given thickness *t*. 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 |