Made from 300D Polyester Ripsop with TPU coating, the bag is hard wearing and 100% waterproof.   The bag attaches securely to your seat post and saddle rails - seat post via the wide velcro strap and saddle rails through the buckles either side of the bag.   The lashings on the top face of the bag allow for additional external attachments.   The roll top closure is simple and effective allowing you to shrink the bag down when you're not utilising the full capacity.