Low-emissivity (Low-E) glass has a microscopically thin coating — typically 50-100 nanometres thick, invisible to the naked eye — that selectively reflects infrared radiation while allowing visible light to pass through.
The science: All warm objects emit infrared radiation. In a heated room, your walls, furniture, and radiators emit infrared that would otherwise pass through the window glass and be lost outside. Low-E coating reflects this radiation back into the room, functioning like a thermal mirror.
Two types of Low-E coating:
Hard coat (pyrolytic): Applied to the glass during manufacture at 600°C. The coating chemically bonds to the glass surface. It's extremely durable and can be used in single-glazed applications, but has a slightly higher emissivity (0.15-0.20) than soft coat.
Soft coat (sputtered/magnetron): Applied after manufacture in a vacuum chamber using magnetron sputtering. Multiple layers of silver and metal oxides achieve very low emissivity (0.02-0.04). Must be protected within a sealed unit as the coating is delicate. This is our standard specification due to superior thermal performance.
Positioning matters: In a double glazed unit, the Low-E coating is always applied to surface 3 (the inner face of the outer pane). This position maximises heat reflection back into the room while protecting the soft coat within the sealed cavity.