The bottle holding bag comes with a strap designed for tubes of 30-60mm diameter and uses grip pads to stop it from slipping or moving while you are riding. The bag itself is made from a lightweight 3-layer waterproof laminate Trilon fabric. With frames featuring less or no bottle mounts it could definitely be helpful for those who like to take a bottle with them to not have to limit their bike choice to only bikes with bottle cage mounts.
The Expedition Downtube Pack sells for $67 // £52 / €59 and is now available from Apidura. You can find out more here.