Low emissivity (Low-E) glass is used mostly when thermal radiation is a consideration.
A special coating is applied to the glass to reflect thermal radiation.
This can help to provide benefits in summer and winter, as it will help to reflect heat away from the house in the summer, whilst reflecting the heat trying to escape the house in the winter back in.
This type of glass does come at a cost, but it can lead to lower energy bills as a result of its ability to reflect thermal radiation.
