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.

By Dhruv Agarwal · · 1 min read

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

PropertyTypical specification
Coating typePyrolytic (hard) or sputtered (soft)
StandardEN 1096, class stated
Coating surfaceNamed by number, typically surface 2
Light transmissionStated as a percentage
Solar factorSHGC value stated for the build-up
UseSoft coat only inside a sealed DGU

Hard coat against soft coat

Pyrolytic (hard)Sputtered (soft)
DurabilityCan face outward, handled normallyFragile; sealed cavity only
Thermal performanceModerateSubstantially better
TougheningStraightforwardNeeds heat-treatable grade
Single glazingPossibleNot suitable
CostLowerHigher

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).

Standards referenced

  • EN 1096 — Coated glass — definitions and classification (CEN-CENELEC)
  • ECBC 2017 — Building envelope — fenestration SHGC and U-value (Bureau of Energy Efficiency)
  • IS 2553 (Part 1) — Safety glass — architectural (Bureau of Indian Standards)

Frequently asked

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.

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.

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.

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