All of the fabrics we use are “waterproof”: coated with urethane inside and treated with a water—repellent outside. We also use YKK splash-proof zippers on the exterior of bags or cover the zipper with a fabric flap to keep water out. However, seams can leak if exposed to significant weather. You can renew the water repellent qualities of your bag with Nikwax. Be wary of other manufacturers claiming that their products are “waterproof” just because the fabrics are coated. If the seams are not RF—welded or heat sealed, they are probably not waterproof.