Looks like headliner material to me. Check above the sunvisors. For some reason this is where they chew a hole and come out. I think they use the sunvisor as a diving board in the summer time.
I read on here to point your sun visors straight down to make it harder for them to use the visors. I know it is not foolpruf, but I started doing it about 8 years ago just out of fear of being jinxed. So far no mice in my car, it sit's outside 3/4 of the year now.
