See my post that's become a sticky, about cap and ball revolvers.
Duro-Felt of Little Rock, Arkansas sells felt that is perfect for wads. Get the 1/8-inch thick hard felt. I bought a large sheet some years ago. Considering that I can get 4 wads per square inch, whether .36 or .44 caliber, I calculated I can make roughly 8,000 wads.
As I recall, I paid around $25 for that sheet of felt.
Even with inflation, you can still get a large sheet of hard, 1/8th inch felt from Duro-Felt for a pittance compared to buying wads from the store.
Melt a couple tablespoons of Gatofeo No. 1 lubricant, SPG, Lyman Black Powder Gold or a mix of lard and beeswax in a pet food can. Add your wads. When they're soaked, removed from heat and allow to cool.
Snap on a plastic pet food cover and you're done.
You can carry the wads to the range in that can, a Zip-Loc, Altoids sour candy tin or shoe polish can (the kind that can be easily opened with greasy fingers).
Cardboard, waxed paper, thin wads, egg carton material and other substances don't soak up enough lubricant in my experience. You need ample lubricant to keep the fouling soft. Wool felt is sponge-like and soaks up quite a bit of lubricant.
Natural sponge, if you could find it 1/8-inch thick, would work too, I guess. I would think that synthetic sponge would leave plastic deposits in the door. Polyester felt is plastic and will leave a build-up of plastic. I've experienced it.
Real wool felt is harder to find but worth the effort.
Duro-Felt is the best source I've found. Alas, the owner may be on vacation. Check her website to see if she's returned.