The 650 Tritan® water bottle is a single walled co-polyester construction that is said to be almost impossible to break. That sounds like a challenge to me. The screw off lid now features a pop up sip spout to make it much easier to drink from on the go. If you need a wide opening you can still unscrew the cap completely. The Tritan® material does not retain flavours or smells from your previous beverage; so it is like drinking from a fresh flask every time, & it is BPA Free. With its translucent finish & measuring markers it is handy for when it comes to using the right amount of water for your freeze dried trekking meals. Made from lightweight, tough Tritan® co-polyester Impact resistant Screw on lid with pop open sip spout Translucent finish with measure markers Doesnt hold on to smells or flavours BPA Free