There are a lot of different types of water bottles on the market, and each one has its own set of pros and cons. But when it comes to leak-proofing, collapsible water bottles are usually not the best option. The main reason why collapsible water bottles tend to leak is because they're made of soft materials like silicone or plastic. When these materials are compressed, they can easily warp and allow water to seep through. There are some collapsible water bottles that claim to be leak-proof, but in our experience, they're not always reliable. If you're looking for a water bottle that won't leak, we recommend sticking with a hard-sided bottle.