Dan,
It is a silicone rubber. Any spray on it just wipes off. Just a quick note on the stencil. My painter opted to mask with tape, after a few tries with the stencil I provided. At the tri star the stencil is quite deep, and hard to get the gun in there. Just an FYI, but the painter I used masks all the time, so it could have been easier for them, and they said it took less time than re-doing the hubcap.
Mike Mizesko
Columbus, OH