If you plan on freezing your bladder, you may want to invest in a second bladder and carry two. I have used Camelbak's for years, and one thing I have noticed is that the more you freeze them, the more likely they are to begin leaking. What happens is, as water seeps into the nooks and seams where the pack is melded together, as it freezes it expands, and stretches these areas to the point that they may become fouled. If this happens, your bladder is useless, as it will leak. Something that you may want to consider doing is refridgerating your bladder overnight about 3/4 full, and as you leave in the morning. put a scoop of ice in it. This is how I always use mine, and I have had cold water all day, and into the evening even in July and August when it is really hot in Central Florida! Plus, if you have bought the second bladder, when you load your bladder into your pack/thermal barrier you can go ahead and have the other ready to go in, and it will be ready when you are!