Cavity wall insulation involves filling the space between the inner and outer exterior walls. You can use a variety of materials for filling the cavity space, including urea formaldehyde expanding foam, cellulose, polystyrene beads and mineral wool or rock wool. Most of our Installers prefer to use polystyrene beads as they are much more effective and provide exceptional insulation. You’ll notice a difference in the warmth of your house straight away.