reflective insulation

In by Mark Goodman

Sheet material with one or both faces having comparatively low heat emissivity, such as aluminum foil. When used in building construction, the surface faces an air space, reducing the heat radiating across the air space.

reflective insulation (Wikipedia)
Radiant barrier is a shiny, reflective building material used to reflect heat radiation.

A radiant barrier is a type of building product that reflects thermal radiation and reduces heat transfer. Since thermal energy is also transferred via conduction and convection, radiant barriers are often supplemented with thermal insulation products that slow down heat transfer via conduction or convection.

Radiant barrier reflects heat radiation (radiant heat), preventing transfer from one side to another due to a reflective, low emittance surface. In building applications, this surface is typically a very thin, mirror-like aluminum foil. The foil may be coated for resistance to the elements or for abrasion resistance. The radiant barrier may be one or two sided. One sided radiant barrier may be attached to insulating materials, such as polyisocyanate, rigid foam, bubble insulation, or OSB. Additionally, reflective tape can be adhered to strips of radiant barrier to make it a contiguous vapor barrier, alternatively, radiant barrier can be perforated for vapor transmittance.

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