Being in SOCAL lotsa water was on my mind when I chose this bag. I've never seen a bladder freeze so "don't know" -- good question for the folks at Camelbak; I suspect it would simply expand to accommodate the ice.

I think that if I was in that kind of weather I'd leave the bladder out and use that space for something else -- maybe a dry set of long underwear (smartwool). My Camelbak Rim Runner weighs 11 1/2 lbs without the water.