The 1000 Tritan® water bottle is a single walled copolyester construction that is said to be almost impossible to break. That sounds like a challenge to me. The Tritan® material does not retain flavours or smells form your previous beverage. So it is like drinking form 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 Tritain® copolyester Impact resistant Screw on lid with wide mouth opening Retaining loop makes it easy to attach to things Translucent finish with measure markers Doesnt hold on to smells or flavours BPA Free