# 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.

## 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)**.

## Frequently asked questions

### What is the difference between soft-coat and hard-coat low-E?

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.

### Which surface should the coating be on?

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.

## Sources

- [ECBC 2017](https://beeindia.gov.in/) — Building envelope — fenestration
- [IS 2553 (Part 1)](https://standards.bis.gov.in/website/published-standards/department-wise) — Safety glass — architectural

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Source: https://hagerstone.com/glossary/low-e-glass