A technical explanation of how the Low-E coating works, its core coefficients, and its documented impact on building energy consumption.
How Does the Low-E Reflective Coating Work?
A metallic or metal-oxide layer just a fraction of a micron thick is deposited on the glass surface, reflecting most of the infrared radiation responsible for heat transfer while still allowing the bulk of visible light needed for natural vision to pass through. The result is an interior space that's naturally lit but doesn't gain nearly as much heat as it would through standard glass of the same area.
Three Coefficients to Understand: U-value, SHGC, and VLT
Thermal transmittance (U-value) measures how much heat passes through the glass — the lower the value, the higher the insulation. Solar heat gain coefficient (SHGC) measures the proportion of solar heat entering through the glass and should be lower in hot climates. Visible light transmittance (VLT) measures how much visible light passes through and should stay relatively high to avoid needing extra artificial lighting during the day. The ideal product balances a low SHGC with a relatively high VLT.
Hard Coat vs Soft Coat Low-E
There are two types of Low-E coating: hard coat (pyrolytic), applied during glass manufacturing at high heat, making it durable enough for single-pane use, and soft coat (sputtered), applied afterward, which delivers higher thermal performance with better SHGC and U-value figures but is less scratch-resistant, which is why it's always used inside an insulated glass unit where it stays protected from direct contact.
The Link to LEED and BREEAM Sustainability Certifications
Sustainability rating systems like LEED and BREEAM set maximum SHGC thresholds and minimum thermal insulation efficiency requirements within the building's overall thermal performance criteria, not just the glass alone. Using Low-E glass with documented coefficients is one of the fastest ways to earn points under the "building envelope performance" category in these systems, provided the test certificates come from an accredited lab and match the calculation methodology the target system requires.
How to Choose the Right Coefficient Based on Facade Orientation
East- and west-facing facades receive intense direct sunlight at specific times of day and need a lower SHGC compared to less-exposed north-facing facades. Ignoring this difference and specifying identical glass across the whole building often results in uneven interior temperatures between rooms facing different directions despite sharing the same cooling system — a common design mistake easily avoided by specifying each facade orientation separately.
