Banner Material
 

So I work in a Ford dealership, and we get those banners that you hang from the ceiling and we were discarding some, I seen that the material looked water proof and resistent to weather, anybody ever use this, I am looking to use it as a grille block and leave off the yellow masking tape as it gets wet and defeats the purpose of blocking the air to go around the grille

Air- and water-proof = all OK.

i have some of that and it is waterproof. would still need something to attach it though, maybe, waterproof tape. aluminum duct tape would work also, even by itself, without the banner.