Organization- Bulletproof Cells

Dana started smashing at the glass with her fists. Her blows did no damage—they’d have to make the glass incredibly strong to contain all these things, he realized—but still she pounded, kicking as well, thrashing, and he had to hold her tight to stop her from hurting herself.
...

As Dana reached back to close the door behind her, there was a shattering burst of machine-gun fire. Bullets struck the door and pushed it closed, and when the handle clicked up she turned the latch, locking it.

Screaming, shouting, she fell back against Marty, and they huddled together behind the metal door. The top half was glass, but it must have been of the same toughened construction as was used in the elevators. Bullets ricocheted off of it, leaving little more than tiny white impact stars where they struck.
...

She moved to the viewing panel, and waved to Marty to join her. There was a pause during which she had time to see the hundreds of spent bullets and casings scattered across the floor, and to think, They really make this glass to last.

- The Cabin in the Woods: The Official Movie Novelization, chapters 10 and 11