This top works well on the Sig. You can set it for drinking or closed (open when you press it against your lips) and it gets the job done...I dropped it when it was on the bottle and the plastic outer cover broke...so don't drop it... 4 stars

My wife and I LOVE our Siggs. We're really trying to cut down on disposable water bottles, and the Siggs are great. I prefer to drink out of the bottle without any kind of cap on it... the ergonomic design of the bottle feels good on your lips, unlike a plastic water bottle or even a Nalgene bottle. But for bike riding, or working out, or anytime you're on the go, you really need to keep a cap on it. And the one that comes with it is fine, but it's hard to suck through. Since the bottle is metal, it doesn't allow for much air to get in while you're sucking, and therefore you need to suck pretty hard. The Sigg Sport cap solves this problem by allowing a generous amount of air into the bottle while you suck, making for a more freely flowing stream of water. Plus, it remains closed at all times except when you press your lips against it. Brilliant design. 5 stars

This cap is much more useful to me than the standard screw open top the bottles come with. I have no problem opening the cap to drink with my teeth. It makes it much easier to use these great bottles while you are on the go. 4 stars

The design of this top is one I have never encountered. I do wish it allowed the water to flow out easier and without as much effort. That said, it doesn't allow any leakage. 4 stars

This cap is not that great. You turn the cap once to enable the flow of water. You apply pressure to the cap to release water. Water flow is pretty slow, If you turn the cap a second time, the entire mechanism is released (for cleaning). If you are trying to use this on a bottle while moving, it is very easy to accidentally release the mechanism. 3 stars