Understanding Low-emissivity (Low-E) glass


Window glass is by nature highly thermally emissive and it lets heat pass through it in both directions. But in extremes of summer and winter, that’s not such a prefered situation. On the hot summer days,  it is preferred that windows reflect back the sun’s heat automatically. Likewise, on the winter days, it would be great if the windows of your home help to stop all that expensive heat from escaping. 

Low-emissivity (low-e) glass is a type of energy-efficient glass designed to prevent heat escaping out through your windows to the cold outdoors. Low-emmisivity (Low-E) glass has a special coating applied to one of the glass faces. 

Low-E provide better thermal performance (U-value)

Low E applied to windows helps block infrared light from penetrating the glass from the outside. In addition, Low E helps keep in your heating/cooling energy. Bottom line: they are much more energy-efficient, helping you save on heating and cooling costs and costs associated with running your heating/cooling systems.

Low-E reduce destructive UV rays

Exposure to direct sunlight can cause many coloured or painted materials to fade. Damage due to fading is caused by mostly ultraviolet (UV) light. The Low-e coatings help reduce UV light. Blocking UV rays save your carpets, furniture, drapes, and floors from fading and sun damage.

How does Low-e work?


Types of Low-E coating

Solar Control Low-E: Blocks solar radiation to reduce cooling costs. Higher-performing glasses are applied or produced by a magnetron sputtered vacuum deposition (or MSVD) soft coat process.

  • Solar control low-E: This type of coatings are designed to limit the amount of solar radiation (heat) that passes into a home or building for the purpose of keeping buildings cooler and reducing energy consumption related to air conditioning.
  • Passive low-e: This type of coatings are designed to maximize solar heat gain into a home or building to create the effect of “passive” heating and reducing reliance on artificial heating.

Low-e coating can be either a ‘hard coat’ or ‘soft coat’ depending on the actual coating process used.

  • A hard-coat Low E glass is a version of the coating which is applied to the glass when it is just coming out of the furnace. The coating is fused onto the glass as it cools down. The hard-coat layer actually becomes "welded" to the glass. This process makes it difficult or "hard" to scratch or remove the hard-coat layer. Often this glass has a blueish tint to it.
  • A Soft Coat Low E is when the coating is applied to the glass after it has gone through the float line process and has cooled down. The coating is fairly delicate or "soft."