The Medio is one of our water resistant, extra durable Arundel seat bags. We make use of sonic welded seams and nylon fabric impregnated with thermoplastic polyurethane. Think frogman raft. The straps are also nylon and wider than usual, like seat belts in planes and cars. A wider strap means more Velcro area for better security. The materials we chose cost more but in exchange, you have a seat bag that should last a good long time.