IMO, it was Duster Wads, Micro-Technologies. Downrange has started making Duster wads now. I have not had a chance to load any of the new ones. I hope they are as good. Kevin at Downrange says they are using the same plastic resins that Micro used.
When I used Claybuster brand I had a lot of plastic build-up in the chokes primarily but a little in the barrel too. All that stopped when I switched to Duster wads. I have not bought any since they sold to DR, but I really hope they are the same as they always have been in the past. I also like the way the Duster went thru the wad guide on the loader, smooth and quiet!
After every outing I swab my fixed choke barrels with a Tico rod and TriFlow. They've never felt a brass brush for 20, 30, 40 thousand rounds. I use Claybuster wads exclusively. Choke tubes are a different story.