Poly patches were a plastic shot cup sort of thing. each side had a hemispherical depression. The end toward the powder acted like the skirt of a hollow base minnie ball to seal the bore. the other end held the ball, with a layer of plastic between the ball and bore wall. It acted like a patch. Early on, there was a problem with the plastic melting and fusing to the bore. It has been decades since I saw any. I never tried them. Cloth was too handy. I knew one or two people who swore by them.
The Butler Creek Corp is apparently still in business in Jackson Hole WY. The web site does not list the poly patches as a current product.
I see a post about them every six months or so. They come up on-line in the auctions frequently.