During the manufacture of cellular insulation, ‘blowing agents’ are used to fill the cells within the insulation with a low thermal conductivity gas, instead of using air. The effect of replacing the air with a blowing agent will reduce the measured thermal conductivity of the material.
In an open cell Insulation, the blowing agent forms irregular pockets that are linked together into a continuous interconnected capillary network. The pockets, or cells, are open and so the blowing agent can quickly dissipate into the atmosphere after manufacture. This could be damaging to the ozone layer, should the blowing agent used be classed as an Ozone Depleting Substance (ODS), such as a CFC or HCFC blowing agent variety.
Immediate transfer of air or water vapour is enabled through the ‘open’ or ‘porous’ interconnected material structure, just like a sponge. Therefore, an example of an open cell foam is the bath sponge where water can easily flow through the entire structure, displacing the air. By the same token, an open cell insulation has a structure that allows moisture and vapour to permeate through it.