According to their website self healing means "...target material expands upon bullet entry and immediately contracts upon bullet exit preventing the target from breaking apart or 'blowing out'. The flexible nature of our material provides a very impressive durability factor and lifespan. Our material will mend its own wounds by closing up entry and exit points up to 98% of the way in ideal situations and or settings."
I've shot mine with everything from .22 to .45 and the holes just close right back up to the size of a pin prick. The entry point is visible due to the friction burn that occurs but other than that it's pretty hard to tell it's been shot.

Apparently I can shoot this thing up to 1500 times or more depending on size of target and rounds used. They're pretty fun so I'm looking forward to seeing how many it will take.