Portmeirion Botanic Garden Cork Trivets

Portmeirion Botanic Garden Cork Trivet Hot Pads Measure about 7 7/8" in diameter and 1/2" thick. *The cork backs are slightly concave on the reverse. I am not sure if that is how they are made or from using them. This does not affect anything, as far as, the use of the trivet goes. Just wanted to be transparent. Let me know if you have ??? Cheers!