I would think they would be made of the same material a windshield is made of. I never saw a windshield exploding.
Windshields (in the usa) are laminated layers of glass and stretchy plastic. All the other windows are tempered (heat-treated) glass. Tempered windows are designed to "explode" into tiny, low-mass blunt cubes, while the laminated windshield tries to entrap all the sharp bits in the plastic layers and remain in as few pieces as possible.
You can get tempered glass to blow out with just the right conditions of temperature and mechanical stress.
Subaru sunroofs have a very slack fit, so they are very tolerant to the body flexing and the mechanism opening and closing. They are not totally rainproof as a result- they are designed to leak a small amount, and they have an internal gutter & drainspout system to deal with this. The net result is 100% rainproof as long as you keep the drain clean.