I leave a little extra space for expansion then seal up the caps. No bursts or capsI keep lots of extra water in my vehicles year round for search and rescue. They freeze in the winter, but I don't think I've ever had a water bottle break. The bottles have a lot of give in them so they will swell and deform, but they don't break. Now I go through them pretty regularly so I'm not sure how the would do if they went through a couple of years of freezing cycles, but a couple of freezes and thaws will probably be no problem.