I was so excited to get these sport caps for our water bottles, however, they have not lived up to my expectations. First, it is very difficult to screw the cap on. Unlike the regular caps, the sport cap is very tight, so it is a struggle to put it on or take it off to refill the bottle. I can't use this cap on my kids' S'well bottles because I know that they won't be able to unscrew the caps themselves to refill their water bottles at school. Second, despite the tight fit, the cap still leaks around the edge (not from the top where you drink from), perhaps because I can't screw it on all the way. The top mechanism works great, so, S'well, please consider redesigning this cap with a better base.