In the Avengers movie, Thor is seen hitting the holding container (designed to contain The Hulk if I'm not mistaken) with his hammer, Mjolnir, which is made of enchanted uru. The glass (?) of the container can somewhat withstand that impact surprisingly. However, it is cracked, and the container is seen partly dislodged from its holding clamps. I suppose the last is why Thor stops hitting it, as he doesn't fancy a fall to the ground while inside the container/holding cell.
But what transparent material is tough enough to (mostly) withstand the impact of the incredibly massive Mjolnir ? I'm afraid the answer will be to simply fit into the movie script, but any other insight will be appreciated.