I hope that it's glass, so that it's more resistant to scratching, but it may be plastic. In any event, I'm very happy to have the solar power, atomic synch, barometer & altimeter. The thermometer may come in handy as well.
Mine seems to be mineral glass. It's not completely impervious to scratching, but it is pretty tough stuff. I don't have the solar power or atomic synch, so I guess I'll have to suffer
. Seriously, battery life thus far has averaged about 3 years (depending on how much you use the bells & whistles), and mine looses roughly 20 seconds per year; I'm pretty satisfied with that.
One thing I don't particularly care for is the length of time it takes the thermometer to adjust to changing temperatures; that being about 20 minutes. Also, it doesn't seem like they took into consideration the sensor's proximity to body heat, as I had to do considerable compensation for it.
Oh, and if you wear long sleeve shirts, forget about getting the sleeve with the watch buttoned