It is important to ensure that heat is not lost from a building's interior through its doors. Efficient glass can reduce energy costs, make homes more comfortable, and help reduce the carbon emissions that damage the Earth's atmosphere. The NSG Group is at the forefront of developing such glass products.

The efficiency with which a window or glazed door prevents heat loss can be assessed by looking at its U_g-value.

The type of glass used in energy-efficient doors is generally known as 'low emissivity' or 'low-e' glass. This improvement over ordinary glass is usually achieved by applying a fine coating to the glass. One well-known and trusted low-e product is Pilkington K Glass™. However, there are other products available with a better U_g value, such as Pilkington _Optitherm™, which must be used within an insulating glass unit.