Barrel and slide. Mags have a metal sleeve. Tenifer coating (I think they have changed it somewhat on the newest generation) is one of the toughest for this type of gun.

From the torture testing info and videos I've seen you could probably leave them in a bucket of water next to the shower and just shake the water out when you need to use them. Not something you would really want to do, but I guess as far as plastic pistols that can withstand moisture Glocks are right there at the front of the race.

I have a model 23 (.40 cal). It's my carry gun.

But my heart still belongs to my S&W revolvers.