Reflective insulation is one or more low emittance surfaces installed in an enclosed air space. The more layers within the air space, the better the performance. Reflective insulation in a wall system can be compared to a double or triple pane window with low-e surfaces. Triple pane windows with low e surfaces perform better than a triple pane window without low e surfaces because of the reduction of radiation (low emittance) across the air spaces.
Air inherently has an R-per-inch value of 5.6, and is an excellent insulator when radiation and convection are controlled. The ASHRAE Handbook has tables with values for various enclosed air spaces (0.5”, 0.75”, 1.5”, 3.5”, etc.) with high emittance surfaces (0.82 for common building materials) and values for air spaces with low emittance surfaces facing the enclosed air space (0.05 for low emittance materials like aluminum). Simply put, adding a low e material makes the enclosed air space perform better. A multilayer reflective insulation system in a wall cavity improves this system by further reducing radiant heat transfer and adding additional “panes”, a two layer reflective insulation could be compared to a double paned window; a three layer to a triple pane window, and so on..
The installation of reflective insulation in an enclosed space reduces thermal radiation to near zero. When the reflective insulation is installed to subdivide an air-filled region then heat transfer by convection is also reduced. Fi-Foil has single layer, two layer, three layer and even honey-comb layer reflective insulation products for various building applications, each with different performance levels and attributes for the particular application. These products also work very well with other types of mass insulation as hybrid systems by using the best attributes of each of the technologies (e.g. spray foam is great for air sealing and can have a high R--value per inch of thickness -- fiberglass and cellulose is an inexpensive material to reduce convection in the cavity). In some wall systems, especially wall cavities larger than 1.5”, a combination of reflective insulation with one or more of these mass insulation products, addresses all the modes of heat transfer -- often more cost effectively than one of the technologies used alone.