I have a small Camelback. The only problem I have with it is that sometimes the water inside the tube freezes since it's exposed to the air outside. The water inside the reservoir bag doesn't freeze though, just what is in the tube. I sometimes wear my Camelback inside my jacket just so that the tube doesn't freeze. Most of the time I just wear it on the outside of everything though. You just have to bend the tube a little bit to break up the ice and then the water will seep through when you try to drink it and melt off the ice.