Mineral Fibre Cavity Wall Insulation Absolute Insulation are approved Installers of InstaFibre Cavity Wall Insulation Material. It is a glass mineral wool that leaves the factory completely prepared to be installed. No chemicals, water or adhesives need to be added at our warehouse or on the site. The material is yellow in colour and the texture resembles cotton wool. InstaFibre also provides the material for loft insulation. It is a glass wool quilt brought in rolls to allow for easier installation and reduces completion time to approximately 1 hour. INSTABEAD Cavity Wall Insulation.