These OHYO collapsible bottles are not only cost effective but also energy saving, dishwasher safe, BPA free, fit in a pocket or bag easily, durable (squish tested 10,000 times,) and hold 500ml. They are even made in the UK (Sheffield)
Although they are recommended for children over 36 months I had no problem with Liv (17 months) drinking from one while we were out and about.
These are a great idea and I would definitely recommend them to Family and Friends.
Disclaimer: I was sent two of these bottles for the purpose of the review, all opinions are my own.