U value is the measure of the insulating capacity of the glass. This represents how quickly heat from hot air (not direct sunlight) will pass through the glass. The lower the U value the better the insulation. Glass with low U values are generally used to keep the warmth in the room, in cold climates or at night.
For example, 4mm clear float glass has a U value of 5.9, whilst ComfortPlus™ has a U value of 3.6. So ComfortPlus™ is a better insulating product than 3mm clear float glass.
Solar Heat Gain Co-efficient (SHGC) is the amount of heat from direct sunlight that passes through the glass. This includes sunlight which passes directly through the glass to the room and the amount of sunlight which is absorbed by the glass and later reradiated to the room. The lower the SHGC, the better it will achieve this. Glass with a low SHGC is best used in areas of direct sunlight, for example to reduce the amount of heat coming through the windows in summer.
For example, our 4mm clear float glass has an SHGC of 0.85, whilst ComfortPlus™ has an SHGC between 0.57 and 0.60 depending on the colour.