The right felt is 100 percent wool and quite stiff. Hobby shops may have wool felt, but all I've ever found is the thin, limp stuff. You need a felt that is stiff, and 1/8" thick.
I've found the right type of felt in two forms: cowboy hats at the local thrift store (check the label to determine if it's real wool) and as stripping for sealing around windows.
Frost King, with offices in New Jersey and Nevada, makes a 100 percent wool sealing strip. It's about 18 feet long, 1/8" thick and about 3-1/2 inches wide. One roll will give you hundreds of wads. Cheap too, at about $3 a roll.
Now, the down side: It's not easily found. The only hardware stores I've found that carry it are Tru-Value. Even then, they don't always stock it. You have to read some Frost King labels to ensure you have the right stuff.
The wool stripping I've found is gray and sold in a plastic bag. It's been a couple of years since I bought any (right now, I'm flush with the right wool) so the packaging may have changed.
Finding the right kind of wool felt is crucial to success.
Polyester felt will melt and leave melted plastic deposits in your bore if you shoot a lot of them. That's why pure wool felt is mandated.
Stiff, hard wool felt is needed because it helps to scrape fouling from the grooves of the rifling.
I've recovered hard felt wads after shooting. Most of them exhibit a negative impression of the rifling, indicating that it reached down into the grooves and scraped out fouling.
Part of my success with wool felt wads may, I believe, be attributed to the lubricant I use. It was once the factory recipe for heeled bullets, loaded in .22 rimfire and .32, .38 and .41 Colt cartridges.
The recipe is:
1 part mutton tallow
1 part canning paraffin
1/2 part beeswax
All measurements are by weight. I use a kitchen scale to measure 200/200/100 grams of ingredients. These are put in a quart, widemouth Mason jar. The jar is placed in 4 or 5 inches of boiling water in a pot. When all ingredients are melted, stir well with a clean stick or disposable chopstick. Allow to cool at room temperature. Hastening cooling by placing in the refrigerator may cause the ingredients to separate.
This creates a very versatile lubricant. I use it for lead bullets in my .44-40 and .45-70 rifles, and soak felt wads in it for my cap and ball revolvers and muzzleloading rifle.
I suspect it would be great for felt shotguns wads and black powder loads.
Find the right type of wool and make your own wads, or buy Wonder Wads. Then soak them thoroughly in the above lubricant. You wont' be disappointed.