Hence the 30% reduction on repacking. The density was there to hold the optimum amount of fuel which in those days was Methylated Spirit which was the same stuff used to prime up the 'Tommy Stoves' used for cooking in the trenches and making tea. Some of those lighters used asbestos wool instead of cotton although I have never owned one of those thank goodness but they show up from time to time as the small aluminum lighters with the removable cap marked 'Tommy' and were a later thing from 1917/18.