A two-component RTV silicone foam that features excellent crack-and-void filling capabilities. Unlike other foams, MRF exhibits uniform cell structure, assuring reproducible, smoketight, fire resistant installations. Minimal pressure during foaming virtually eliminates shrinkage of the cured material. The elastic properties of the foam readily accommodate minor vibration of the pipe, conduit, etc. without loss of system integrity. Used in a 1:1 mix ratio, MRF, when properly mixed, expands 2 to 4 times its original volume, filling available spaces and forming an effective barrier against fire, smoke and water penetration.