Made of innertube rubber material, weatherproof and low maintenance. If it catches dirt, just wipe off surface with wet cloth or sponge. Dries in minutes. There are two options in mounting to the bike, under the saddle or on the seat tube. It can hold spare inner tube and portable tools. External pockets is useful to keep small litters or coin purse. The locking strap is adjustable by velcro for a snag fit and prevent “tail wagging” as you ride. For those keen on function and design for ecoethical lifestyle.