IsoBacker is specifically designed to maintain high acoustical ratings in fire rated walls. It is easy to apply and will stay resilient (will not harden). Model IsoBacker is UL classified for both metallic and non-metallic outlet boxes to prevent the spread of smoke, fire and toxic gases. The putty pads are sized to cover standard size outlet boxes and are designed to work with Kinetics Model IsoMax sound clips and other sound rated wall assemblies.