LowEmissivity

Low emissivity, often abbreviated as low-e, refers to materials or coatings designed to reduce the emission of infrared radiation from a surface. In architectural glazing, low-e coatings are thin, transparent layers applied to glass that reflect a portion of thermal infrared energy while allowing visible light to pass through. This reduces heat transfer between indoors and outdoors, improving energy efficiency and reducing heating and cooling costs.

Low-e coatings work by creating a barrier to radiative heat transfer. They are typically multilayer thin films produced by vacuum deposition. There are two broad categories: hard-coat (pyrolytic) coatings, which are durable enough to be tempered or laminated during manufacturing, and soft-coat (vacuum-deposited) coatings, which offer higher performance but require a protective overcoat. Common materials include silver-containing multilayers or dielectric pairs of metal oxides and sulfides designed to minimize infrared emissivity while preserving visible transmittance. Emissivity values for coated glass can be as low as around 0.04–0.08, compared with about 0.84 for ordinary clear glass.

Applications and performance: In windows, low-e coatings improve U-value and the solar heat gain coefficient (SHGC) depending on the design, enabling winter heat retention and summer solar control. In automotive glazing and building façades, coatings are chosen for a balance between light transmission, glare, and thermal performance. Some coatings are spectrally selective, reflecting infrared radiation while transmitting visible light, producing energy savings without darkened interiors.

Limitations and considerations: Low-e coatings add cost and can reduce visible brightness if not optimized. Durability and maintenance vary by coating type; hard-coat products are typically scratch resistant, while soft-coat configurations may require protective layers. Standards and testing for emissivity, transmittance, and SHGC are provided by industry bodies and building codes.