Low-E glass is coated with an ultra-thin layer of metal that you can see through and provides insulating value.
The E is for Emissivity
Low-E glass is a special glass that has a low rate of emission. In other words, if there is a heat source inside or outside your house, the glass bounces the heat from that object back away from the glass.
In the summer, the sun heats things up outside of your house. This heat radiates from the objects outside your home and tries to get into your house through the path of least resistance, that being the glass. With Low-E glass much of this heat bounces off the glass and stays outside.
In the winter months, the Low-E glass in your home will bounce the heat given off by the furnace and all the objects which the furnace has heated into the room.
The Two Types of Low-E
Hard coat Low-E glass is manufactured by pouring a thin layer of molten tin onto a sheet of glass while the glass is still slightly molten. The tin actually becomes “welded” to the glass. This process makes it difficult or “hard” to scratch or remove the tin. Hard coat low-e glass often has a blueish tint to it.
Soft coat Low-E glass, on the other hand, involves the application of silver, zinc or tin to glass in a vacuum. The glass enters a vacuum chamber filled with an inert gas which is electrically charged. The electricity combined with the vacuum allows molecules of metal to sputter onto the glass. The coating is fairly delicate or “soft.”
R Values / (Resistance to heat Loss)
The higher the R value of a material, the better its insulating qualities. The soft coat process has the ability to reflect more heat back to the source and typically has a higher R value.
GLASS R VALUES
|Type of Glass||R Value|
|Single Pane regular glass||0.85|
|Clear Insulated Glass 7/8 inch overall thickness||2.08|
|Hard Coat Low-E insulated glass||2.45|
|Hard Coat Low-E insulated glass with argon||2.75|
|Soft Coat Low-E insulated Glass||3.50|
|Soft Coat Low-E insulated glass with argon||4.35|