Low-E Glass: Coated Glass That Controls Heat
Low-E — low-emissivity — glass carries a microscopically thin metallic coating that reflects heat radiation while letting visible light through. It reduces heat transfer through the glass, and solar-control variants also cut the sun's heat gain — which is what matters most in hot Indian climates.
By Dhruv Agarwal · · 1 min read
Why it matters
Glass is usually the weakest part of the envelope thermally. A low-E coating changes that without making the glass dark, which is why it is central to meeting ECBC targets while keeping daylight.
How it works in practice
| Type | How applied | Use |
|---|---|---|
| Soft-coat | Vacuum deposition after manufacture | Inside DGUs, best performance |
| Hard-coat | Fused during manufacture | Single glazing, durable |
| Solar-control low-E | Soft-coat tuned to block solar heat | Hot climates |
Common mistakes
- Using soft-coat in single glazing. The coating is exposed and degrades.
- Coating on the wrong surface. Performance changes significantly.
- Choosing on appearance only. Check SHGC, U-value and light transmission.
Standards referenced
Fenestration performance under ECBC 2017. Safety glass under IS 2553 (Part 1).
Standards referenced
- ECBC 2017 — Building envelope — fenestration (Bureau of Energy Efficiency)
- IS 2553 (Part 1) — Safety glass — architectural (Bureau of Indian Standards)
Frequently asked
Soft-coat low-E is applied in a vacuum after the glass is made; it performs better but is fragile, so it must be sealed inside a double glazed unit. Hard-coat is fused onto the glass during manufacture; it is tougher and can be used in single glazing, but performs less well.
For solar control in a cooling climate, the coating usually sits on surface 2 — the cavity-facing side of the outer pane — so solar heat is reflected before it enters the cavity.
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