Tyvek Reflex heat reflective membrane helps to improve thermal efficiency by reflecting radiant heat in summer, and reducing convective heat loss in winter. Tyvek Reflex is a strong, water-resistant breather membrane with a metallised surface. It is suitable for use in any wall system that requires secondary protection from external moisture. This low emissivity membrane is particularly effective in lightweight wall construction such as timber or metal frame systems, and is also popular for masonry and internal insulation upgrades. Properties Length: 100m. Width: 0.48m. Roll size: 48m2. Weight: 4.2kg. Thickness: 220m. UV exposure: 4 months. Emissivity: 0.09. Composition: high density polyethylene with metallised surface. Certification: BBA Certified. CE Marked. Thermal performance The emissivity of a material is the ability of its surface to emit energy by radiation. The lower the emissivity value, the more reflective the material is “ and the better the material performs as a thermal insulation layer in combination with an air gap. With an emissivity value of just 0.09, Tyvek Reflex reflects 91% of radiant heat for greater thermal comfort and enhanced airtightness. This in turn reduces the constructions overall thermal transmittance, or U-value.