In summer, radiation from the sun strikes the outer surfaces of walls and ceilings and is absorbed causing the surface to heat up. This heat flows from the outer wall to the inner wall through conduction, which is then radiated again, through the air spaces in the building, to other surfaces within the building. Radiation between surfaces is through invisible, infra-red heat rays.
Reduction of heat transfer from outside to inside of a building lowers the cost of cooling during summer days. A reflective insulation system helps the process. It is typically formed by layers of aluminium or a low emittance material and enclosed air spaces, which in turn provide highly reflective or low emittance cavities (Air bubble film) adjacent to a heated region.
The performance of the system is determined by the emittance of the material(s), the lower the better, and the size of the enclosed air spaces. The smaller the air space, the less heat will get transferred by convection. Therefore, to lessen heat flow by convection, a reflective insulation, with its multiple layers of aluminium and enclosed air space (INSUreflector), is positioned in a building cavity (stud wall, furred-out masonry wall, floor joist, ceiling joist, etc.) to divide the larger cavity (3/4” furring, 2” x 4”, 2” x 6”, etc.) into smaller air spaces. These smaller trapped air spaces reduce convective heat flow.
Reflective insulation differs from conventional mass insulation in several ways:
- Reflective insulation has very low emittance values ‘E-values’ (typically 0.03 compared to 0.90 for most insulation), thus it significantly reduces heat transfer by radiation.
- A reflective insulation does not have significant mass to absorb and retain heat.
- Reflective insulation has lower moisture transfer and absorption rates, in most cases.
- Reflective insulation traps air with layers of aluminium & air bubble film plastic as opposed to mass insulation that uses fibres of glass, particles of foam, or ground up paper.
- Reflective insulation does not irritate the skin, eyes, or throat and contain no substances, which will out-gas.
- The change in thermal performance due to compaction or moisture absorption, a common concern with mass insulation, is not an issue with reflective insulation.
