If you're looking to keep your CamelBak from freezing while skiing, there are a few things you can do. First, make sure that the reservoir is properly insulated. You can find specially-designed CamelBak reservoirs that come with built-in insulation, or you can insulate your existing reservoir with a sleeve or wrap. Additionally, be sure to keep the reservoir filled as much as possible - this will minimize the amount of air inside that can cause freezing. Finally, if it's really cold out, consider using water bottles instead of a CamelBak - they'll be less likely to freeze.