Clear plastic pop bumper skirt, or wafer, used in most pinball manufacturers' pop bumper assemblies.
New, tough poly-carbonate material for great durability and responsive actuation.
It's a good idea to change all bumper skirts simultaneously for a good color match on the new plastics.
Old plastic discolors and becomes brittle with age. New skirts have consistently bright colors.
Reference:
Williams 03-6035-4
Bally C-790-11
Gottlieb C-10433-RED
A-1218