This is a very sturdy rubber, 1/2" thick, cobbler's/diy worker's mat. These are handy when using a punch or cutting device as it protects the surface you are using it on, and also is firm enough to help achieve a perfect punch or cut. It creates a great work station when using tools like an awl, and serves as a protection for the surface you are working on.
The picture shows other tools that are not included. The tools are in the picture to get a size perspective.

dimensions: 10" x 10" square
color: black