Thermalite is most commonly used in cross-matching time fuse. You cut a slit in the end of the time fuse, put in a piece of Thermalite and it closed with string. Or, punch a hole perpendicular to and through the powder core of the time fuse, threading a piece of Thermalite through the hole, then gently squeezing the safety fuse with pliers or similar to bring the powder core into contact with the Thermalite.