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Performance metrics & physics

Emissivity Rating

Emissivity rating is the measured tendency of a surface to emit thermal radiation; low-emissivity (low-e) films re-radiate less heat into the cabin or room interior.

Emissivity is a number between 0 and 1, where 0 is a perfect reflector and 1 a perfect emitter (black-body). Untreated glass has emissivity around 0.84. A low-e coating drops it to 0.04–0.20.

In architectural double glazing, a low-e coating on an internal surface dramatically reduces heat radiated outward (heating climates) or inward (cooling climates). For Singapore cooling, it cuts radiated heat from sun-warmed glass into the room.

For automotive single-pane glass the effect is more modest, but still measurable in cabin thermal comfort.