Reflective insulation is usually shiny aluminium foil laminated onto paper or plastic and is available as sheets (sarking), concertina-type batts and multi-cell batts. Together these products are known as reflective foil laminates.
Dust settling on the reflective surface will greatly reduce performance. Reflective surfaces should be faced downwards or kept vertical. The antiglare surface of single sided foil sarking should always face up.
Reflective insulation mainly resists radiant heatflow due to its high reflectivity and low emissivity (ability to re-radiate heat). It relies on the presence of an air layer of at least 25mm next to the shiny surface. The thermal resistance of reflective insulation varies with the direction of heat flow through it