Here’s a bottle that can easily convert into a sippy cup and then again into a bottle as per your need. Just fit in the Avent adapter and spout and there you have a sippy cap and remove it and you have a stainless steel bottle.

Not just this, the Kleen Kanteen Bottle will also grow up with your kid. Yes, when your child outgrows the age of sippy cups, just replace the spout with the stainless steel cap and he has a bottle that he can take to his school.
The 355 ml bottle is made of high quality, food grade 304 stainless steel, while the adapter is made of #5 polypropylene plastic and comes along with two Avent spouts.
Via: LifeWithoutPlastic