The Arundel Medio Seat Bag makes 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. All three are slightly roomier than our time-proven corresponding sized Uno, Dual and Tubi.