Once, I developed a hole in my Olfa Mat. Here is why: I had a very sharp blade. I cut from the back side of the mat. I didn’t know it is possible to cut half way through the mat. The cut on the back lined up perfectly with a cut on the front, and there was a hole all the way through!
So, never cut on the back side of your Cutting Mat.
I am more careful with my new mat, only cutting from the green side. 😮 )