Bubble Insulation Properties
Basic Properties of Soap Bubbles used as Thermal Insulation
The bubbles are generated at an average diameter of 6mm, thus in a 500mm cavity we have an average of 83 still air boundaries. This could be equated to 83 glazing layers, however the properities of bubbles are surpisingly complex and different to what we might first imagine. Research indicates that the primary thermal energy transfer mechanism within the Solaroof cavity is vapour migration from the warm inner to cold outer skin. The bubble walls, which are a liquid, do provide a conductive path, but the rate of loss contributed by this is very small because very little of the cavity space volume is liquid and the conductive path is long.
Vapour must migrate from bubble wall to bubble wall - but the temperature difference across an individual bubble is very small and so the rate of transfer is low. The bubbles are also opaque to thermal radiation emitted from the building interior and warm glazing (long wave IR) and to solar IR and so they greatly alter the transfer of energy by radiation, which is much more powerful then the conductive transmission. It is also interesting to note that as the temperature of bubbles approaches zero, vapour within a bubble also approaches zero, thus a cold bubble mass is actually the best insulator. However cold bubbles do not tramsit thermal energy stored in the thermal mass back into the building environment. They can however be utilised in a double cavity configuration for use in extreme cold climates.