Metacaulk® Box Guard™ is a one component fire rated pad for use in electrical boxes. It is inserted on the inside back wall of an electrical box and is a highly intumescent firestop material. Saves labor costs. Box Guard™ is an economical alternative to putty pads. Great for use on retrofit jobs. STC Rating 53*. Complies to Required Environmental Testing of Accelerated Aging and High Humidity as per UL 1479 Fire Test of Through-Penetration Firestops. US Patent Number 6,207,085. *Tested in a UL 411 wall assembly/section to ASTM E90.