What is low-e glass?

Low-e stands for low-emissivity and refers to a special coating that reduces the heat transfer of a window assembly. Low-e coated products that reduce solar heat gain can be produced by adding a metallic coating either while the glass is in a molten state or by applying to the glass after it has cooled to a solid state. Low-e glass is readily available from all the glass and window manufacturers. The coatings typically add about 10% to the cost of a window but costs vary by product type, by manufacturer, by retailer and by location.

Based on how it is manufactured, low-E glass can fall into two categories: pyrolytic deposition (hard coat) and vacuum deposition (sputter coating) low-E. The difference between the two is that the pyrolytic deposition method applies various metals to molten glass during the float glass manufacturing process. Vacuum deposition, on the other hand, applies various metals off-line in a large vacuum chamber. Pyrolytic coatings have higher solar heat gains and U-values and may not meet energy codes. They also can be less crisp in appearance compared to sputter coatings. Sputter coatings are offered in a wide variety of color and performance options, including post-temperable versions, and can meet and exceed energy code requirements.