I am not happy using plastic sippy cups for my son, but I got a sigg and it leaks everywhere if tipped over and I regret paying all the $ for it. I use a very sturdy glass milk bottle (embarrased - can't remember the company's name, but I think its pretty common something family farms?) anyway, they have great glass bottles that we reuse for water bottles for grown ups. I'm just thinking it would be so fantastic if there was some kind of sippy lid you could buy that could just be screwed on to a stury glass bottle? Any such thing?