Welded rather than sewn seams are the only way make 100% waterproof backpacks. We WELD the seams of a highly polyurethane coated nylon fabric to make pack liners. These liners are then sewn into our backpacks using the welded tabs. By using a liner on the inside, we can give you more cycling specific features on the outside like blinker mounts, pockets, pocket attachment points, compression straps and u-lock holsters. These liners also contain large welded Velcro panels which are used to attach accessory padded laptop pouches to protect and secure your digital world.