Question about material

my wife bought some hard rubber for me to make ink stamps with. I looked on the materials list and there is no hard rubber. What should i use? I was thinking linoleum but that is harder than rubber. Any suggestions?

I found out that hard rubber isn’t the best material for cutting on the x-carve. It works but there’s a lot of cleanup as it tends to roll to the side instead of cutting clean. Other than that it worked great.