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How does Low E glass help save energy and reduce costs?

The way Low E glass coatings work is  by reflecting or absorbing IR light (heat energy). How well the window performs is based on the thickness of the Low E coating and the position in the window (#2 or #3 surface)

  • During the cold months when you want to reduce heat loss and energy costs, the Low E coating needs to be installed on the #3 surface of an insulated glass unit (IG). This way the Low E coating can reflect IR heat from inside the room to help reduce energy loss.. View flash demo
  • To reduce solar gain and cooling costs throughout the warmer months, the Low E coating should be installed on the #2 surface of an IG unit in order to reflect or absorb IR heat from the outside View flash demo

Low E terminology. Make an informed choice by reading about the Low E selections: solar selective Low E, hard-coat, soft-coat, sputtered, and pyrolytic.


CVD, or chemical vapor deposition, is one of two main technologies used to manufacture Low Emissivity glass. In the CVD process, vapor directed to the hot glass surface reacts to form a ceramic coating. The resulting Low E product is often referred to as "hard coat".


Emissivity refers to the ability of a surface to absorb or reflect heat. An energy efficient glazing technology, Low Emissivity glass is a poor absorber of heat!

Hard coat

Also known as "pyrolytic", hard coat refers to Low E glass manufactured via the CVD process. Because the coating is covalently bonded to the glass, hard coat Low E is extremely durable.


MSVD, or magnetron sputtering vacuum deposition (also known as "sputtering"), is one of two main technologies used to manufacture Low emissivity glass. In MSVD, a metal or ceramic target bombarded with ions releases atoms to form a thin coating on a sheet of glass. The resulting Low E product is often called "soft coat" or "sputtered".


See "Hard Coat" or "CVD"

Soft coat

Also know as "sputtered", soft coat refers to Low E glass manufactured via the MSVD process. Less durable than its hard coat counterpart, soft coat Low E requires special storage and handling to prevent damage to the coating.

Solar heat gain coefficient (SHGC)

The Solar Heat Gain Coefficient (or SHGC) refers to a window's ability to transmit solar radiation. The SHGC ranges from 0-1. A value of 0 indicates that the window functions like a wall, essentially preventing any solar energy from entering the building. A value of 1 indicates that the window functions like an opening, allowing all solar energy in. In cold climates, a high SHGC can lower heating costs by using passive solar heating. In warm climates, a low SHGC is desired to keep unwanted heat out and reduce cooling costs.

Solar selective Low E

Specifically designed to enhance comfort in warm climates, solar selective Low E is a Low E glass with a low solar heat gain coefficient, like Arkema's Sun ETM.


See "soft coat" or "MSVD"


Also known as the K-value, the U-value is a measure of a window's ability to transfer heat (usually given in W/m2K or Btu/hr ft2 oF). Windows with a low U-value, like Low Emissivity windows, are efficient insulators against heat loss.