Between 10-50% of a home's energy loss is believed to occur through its windows and doors, with 90% of the energy lost through windows being lost through the glass itself, according to some estimates. This is an undeniably significant amount of energy to be wasting through such a small portion of your home's structural integrity. In an attempt to remedy this situation, the first low-emissivity glazing solution was introduced to the market in 1975.

Thermal energy is typically the focus of attention when describing the surface's emissivity, which is the amount of energy emitted at specific wavelengths by that surface. A material is assigned a numerical thermal emissivity value ranging from 0 to 1, with a perfect reflector having an emissivity of 0 and a perfect absorber having an emissivity of 1. A perfect reflector has an emissivity of 0 and a perfect absorber has an emissivity of 1.

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The thermal emissivities of metals, such as silver and aluminum, are less than 0.05, whereas standard clear glass has an emissivity of approximately 0.9, making it one of the higher emissivity materials available. To put it another way, standard glass has a thermal emissivity of 0.9, which means that it allows 90% of thermal energy to pass through it while reflecting the remaining 10%. As a result, it is clear that window glass requires assistance in reflecting heat back into the home.

This is where low-emissivity insulating glass comes into play. It is basically clear glass with a microscopic, transparent coating applied to the surface that is more effective at reflecting heat than the quisure insulated glass itself, resulting in a composition that has lower thermal conductivity than standard glass. Therefore, glass with a low E coating keeps your home warmer by reflecting a greater proportion of the heat back into your home, and it can also keep you cooler by reflecting solar thermal energy from the outside world.

There are two types of coatings available: "soft-coat," which is applied to the insulated glass door off-line in a vacuum chamber at room temperature and sealed within an IGU, and "hard-coat," which is fused to the surface of the low-emissivity  glass     while it is being manufactured. Because it has a lower emissivity and is more commonly used in the UK market, we'll be concentrating on soft-coat coating for the purposes of this article.