At mimijumi, we are constantly evolving and looking for ways to improve our bottles. We think we've done a pretty good job so far with just about everything... but nobody is perfect. Recently, we surveyed some of our customers and the one complaint we got back was about the cap not staying on securely. We totally agree this is a problem. The original cap design was not so great. We've made some changes to try and make it better, but truthfully it's still not where we'd like it to be. The cap does work as intended... but only if you use it correctly. In our minds, you shouldn't need a tutorial to use the cap correctly, so we're still working on changing the design again to make the cap usage easier and 100% intuitive. However, in the meantime, here's a quick video showing you how to put the cap on your mimijumi and have it stick!