Mass Transport into a Three-Component Composite Subjected to a Temperature Gradient

If considered on the basis of cellular structure alone, rigid polyurethane foams (PUF) consisting entirely of closed cells are ideal materials for thermal insulation applications. However, the low load-bearing capacity of the material and the vulnerability of the cell membranes make it virtually impossible for the foam to be used on its own. Therefore, technical insulations are usually based on composites consisting of (a) a substrate, which by virtue of its superior engineering properties supports the insulant (PUF), (b) A liner, which reduces ingress of species which might damage the insulant if they were to come into contact with it, and (c) the insulant itself. Examples of such composites are the insulation panels used in the building industry.