Insulated Glass Units are manufactured the same as Double Glazed Units but have Low E Glass types are on inner pane to assist in the conservation of fuel and energy, with outer pane clear, obscure, tinted or self cleaning.
Pilkington EnergiKare Units are made up of two types of glass, Pilkington K Glass (low E Glass) on innerpane which stops heat escaping and Pilkington Optiwhite, an extra clear glass (Low Iron) which allows more solar heat in through the window. The use of argon gas with warm edge spacer bars further improves the thermal performance down to 1.5W/m2K.
PLANITHERM TOTAL+ (low E Glass) can be used on inner pane to achieve lower U values, down to 1.2 W/m2K
PLANITHERM TOTAL One even lower U Values 1.0 W/m2K
Sealfast also manufacture Guardian Climaguard glass units again U values down to 1.2W/m2K