Lil' Topper is no-spill top for bottled water that will fit 99% of the bottles available through your local retailers.  (This 2pk comes with 1 type B thread and 1 type Y thread so you're sure to fit all types of bottles.) 

It's purpose is to help your twins get the water they need without soaking everything around them.

The patented valve the restricts the flow of water until the child sucks hard enough to open the valve. This can only happen when the child's mouth is around the opening.

Clothes, car-seats and furniture stay dry.

The wavy part around the outside of Lil' Topper was designed with three purposes in mind. 1) At 2" in diameter, it's not a choking hazard. 2) The big diameter gives the adult plenty of leverage to tighten it onto the bottle. 3) The waves are just the right size to be a great teething area for the little one.

Lil' Topper is 3 or 4 times smaller than the smallest "sippy cup." This means you'll have to carry a lot less when you're headed out with your twins.

With a couple of Lil' Toppers tucked away in your diaper bag or purse you don't have to worry about what your twins will drink if there's a change of plans for the day's activities. Bottled water is available nearly everywhere.

You can easily refill a water bottle too, at a fountain, a tap, or home water dispenser.   Great for an active twins family!!