Marine Firestop Putty is designed to seal small to medium size cable openings in fire-rated divisions. The following charts give the number of 3M pillows needed to completely firestop an opening that cable tray passes through. Working in inaccessible openings is often cumbersome. Ready-to-install kit for complete cable or blank firestop installation Tested up to 4 hours for fire-rated through penetration systems in accordance with ASTM E814 (UL 1479) No gasket required to ease installation process For industrial/occupational use only. These firestop pillows are specifically.