 During construction of new buildings, cavities are often filled with glass fiber wool or rock wool panels placed between the two leaves (sides) of the wall, but many other building insulation materials offer various advantages and many others are also widely used.For existing buildings that were not built with insulated cavities, a fibrous material such as cellulose insulation or glass wool is blown into the cavity through suitably drilled holes until it fills the entire wall space.Foam can also be used for this purpose.