I used to buy these through Napa but the local store no longer stocks them. I haven't been able to destroy any yet. They're a nice, heavyweight, fabric-backed rubber that's nearly 1/4 inch thick. I have installed several kits and have not yet seen a single bubble like the photos in the previous review. This is the best value for money! Much better than any of those cheap flimsy plastic valves everyone is trying to sell you these days!