How can I tell if the hardboard sheets I purchased at Home Depot is tempered or not? Bought sheets at different times; one is smooth on both sides, while the other is not. Iam using in my shop, and wish to use tempered hardboard only. I read once that one could tell the difference by looking at the stack-tempered has a red stripe on the ends,and a green stripe was non-tempered. I no longer see these stripes on the ends. Thanks for any thoughts.