Heat loss is normally measured by the thermal transmittance or U value, usually expressed in W/m²K. In its most basic terms, the lower the U value, the greater the thermal insulation. U values for insulating glass units are determined in accordance with BS EN 673.  

An insulating glass unit comprising 4 mm Pilkington Optifloat™ Clear outer pane, 16 mm argon gas-filled cavity and 4 mm Pilkington K Glass™ inner pane has a centre pane U value of 1.5 W/m²K.  

An insulating glass unit comprising 4 mm Pilkington Optifloat™ Clear outer pane, 16 mm argon gas-filled cavity and 4 mm Pilkington K Glass™ S inner pane has a centre pane U value of 1.2 W/m²K. 

An insulating glass unit comprising 4 mm Pilkington Optifloat™ Clear outer pane, 16 mm argon gas-filled cavity and 4 mm Pilkington Optitherm™ S1 Plus inner pane has a centre pane U value of 1.0 W/m²K.  

For more information on our range of products for thermal insulation, please click here. 

U values for any of our double and triple glazing combinations can be calculated using our Spectrum online tool. Registration is free and easy. Please click here to register.