Low-E glass is achieved by coating glass during the manufacturing process. The purpose of this coating is to increase thermal efficiency by limiting the amount of heat that is transferred through the glass. By reflecting the heat back to its source, it keeps your home cooler in the summer and warmer in the winter. Look for windows that have a low U-Value. The lower the U-value, the better the item is at reflecting heat back to its source, and the more you’ll save on your utility bills.
There are 2 types of Low-E coatings on glass – they are known as Soft coat and Hard coat.
Soft coat Low-E is achieved by subjecting a finished piece of glass to a chemical process which leaves a thin metallic coating on 1 side of the glass. This method produces an arguably thermally superior product than its hard coat counterpart, which is why it is the most common form of coating. The only downside to the soft coat is that is not a very durable coating. As such, it is best utilized in between 2 panes of glass in an Insulated Glass Unit where it will not be directly exposed to the environment.
Also known as “Pyrolytic”, Hard coat Low-E is achieved by subjecting glass to a chemical process during its production. The resulting product is much more durable than soft coat, which is why it’s primarily used in single-glazed applications where the glass would be open to the environment. However, the chemicals can group together when applied to the melted glass, which can leave a somewhat uneven distribution and results in a slightly inferior thermal performance compared to soft coat.