Coal extenders are materials which will hold a coal for a long time. They are very useful for carrying fire for an extended period of time, perhaps while on the move. They could also be used when you are in the process of starting a fire, but don’t yet have all the material needed to actually make the fire. The coal extender could be used to hold the coal while you go out and collect more materials. Or, let’s say you find that your tinder bundle simply won’t blow into a fire – perhaps it’s too damp. A coal extender will allow you to go search for more suitable materials for a tinder bundle without having wasted all that energy you expended just getting the coal (say by using a hand drill or bow drill).