I still have some green plastic Poly Patches made by Butler Creek in the early 1980s.
I stopped using them about then, because they just didn't deliver the accuracy compared to a linen patch.
Also, being plastic, they wouldn't hold any moist lubricant to keep fouling soft.
Poly Patches were wasp-waisted, and I seem to recall that you should seat the ball on top of one, then gently push the Poly Patch halfway into the muzzle.
While there, apply a little grease around the indented waist, then seat it down on the powder.
I recall that the ads of the 70s and early 80s claimed that the Muzzleloading U.S. Olympic team used them in competition with stunning success.
After the ads ran a year or two, I never again saw any mention of the Poly Patch associated with the muzzleloading team.
I still have about 25 of them.
They're green plastic, and made with a cup on each end so it doesn't matter which end you choose to start in the bore.
The lead ball is just very slightly covered by the cup of the plastic patch.
Recovered plastic wads show a reverse of rifling on the plastic, so apparently they gripped the rigling well enough.
But I used them one summer and went back to lubricated linen patches, they were cheaper and shot better in my CVA Mountain Rifle in .50 caliber.
I believe the Poly Patches were color coded: Green for .50 caliber, brown for .45 caliber and red for .54 caliber. Or so I seem to recall.
I threw away the plastic sack they came in years ago, so I'm relying on my grumpy ol' desert cat memory.