I use thicker waxboard from orange juice cartons.
I think that they're stiffer than wool wads which can create a tighter seal, and they exit the barrel relatively unscathed.
The main difference is that they don't absorb lube. However the American Pioneer powder that I load with does not recommend using lube with it.
I tried the egg carton material and didn't really like it.
Do-It-Yourself Felt Wad Making
In red96ta's case, I wonder if a cap came off during the firing sequence which created an exposed nipple. In that case simply make sure that the caps are seated snug by using a push stick. And try to find the best fitting caps for the Treso nipples.