# Reflective Coated Glass — Solar Control Coatings

> Reflective coated glass is float glass carrying a metallic or metal-oxide coating that reflects part of the solar spectrum, used to meet an SHGC target on glazed facades. The key choice is hard (pyrolytic) coat, durable enough to face outward, or soft (sputtered) coat, which performs better thermally but must sit inside a sealed double-glazed unit.

## What it is

Float glass carrying a **metallic or metal-oxide coating** that reflects part
of the solar spectrum. It is the primary tool for meeting an SHGC target on a
glazed Indian facade.

## Specification at a glance

| Property | Typical specification |
| --- | --- |
| Coating type | Pyrolytic (hard) or sputtered (soft) |
| Standard | EN 1096, class stated |
| Coating surface | Named by number, typically surface 2 |
| Light transmission | Stated as a percentage |
| Solar factor | SHGC value stated for the build-up |
| Use | Soft coat only inside a sealed DGU |

## Hard coat against soft coat

| | Pyrolytic (hard) | Sputtered (soft) |
| --- | --- | --- |
| Durability | Can face outward, handled normally | Fragile; sealed cavity only |
| Thermal performance | Moderate | Substantially better |
| Toughening | Straightforward | Needs heat-treatable grade |
| Single glazing | Possible | Not suitable |
| Cost | Lower | Higher |

## What to state on the order

The coating **name and manufacturer**, the **surface number**, the **glass
thickness and build-up**, the **light transmission**, the **SHGC for the
complete unit** — not the monolithic pane — and whether the glass is
heat-strengthened or toughened.

A coating performance figure quoted for a single pane does not describe the
double-glazed unit that will be installed.

## Where projects go wrong

- **Surface number unstated**, so the unit is assembled with the coating in the
  wrong position and the performance calculation no longer applies.
- **Soft coat exposed** on a single-glazed application. It degrades.
- **SHGC quoted monolithic**, then used in an ECBC compliance calculation.
- **Reflectance chosen purely visually**, without considering glare onto
  neighbouring buildings and roads.
- **Mixed batches across one elevation.** Coating colour varies subtly between
  production runs and shows on a continuous facade.

## Standards referenced

Coated glass classification under **EN 1096**. Fenestration SHGC and U-value
targets under **ECBC 2017**. Architectural safety glass to **IS 2553 (Part 1)**.

## Frequently asked questions

### What is the difference between hard coat and soft coat?

Hard coat, or pyrolytic, is applied while the glass is still hot on the float line, so the coating fuses into the surface and is durable enough to face outward and be handled as ordinary glass. Soft coat is sputtered onto cooled glass in a vacuum and performs considerably better thermally, but it is fragile and must sit inside a sealed double-glazed cavity where it cannot be touched or weathered.

### Which surface should the coating be on?

In a double-glazed unit for a hot climate, solar control coatings normally go on surface 2 — the inner face of the outer pane — so solar energy is rejected before it enters the cavity. Moving the same coating to surface 3 changes the unit's performance substantially. The surface number must be stated on the order; assuming it is a common and expensive error.

### Do reflective facades cause glare problems?

They can, and in dense Indian cities it is a real complaint. A highly reflective elevation throws sun into neighbouring buildings, balconies and roads, and residents notice. Some development authorities now question highly reflective specifications for this reason. Moderate reflectance with a good spectrally selective coating usually achieves the SHGC target without turning the building into a mirror.

## Sources

- [EN 1096](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Coated glass — definitions and classification
- [ECBC 2017](https://beeindia.gov.in/) — Building envelope — fenestration SHGC and U-value
- [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/materials/reflective-coated-glass