We hesitate to call these bags "waterproof" and instead use the term "water resistant". The bags are lined with either 100% waterproof PUL fabric or 100% waterproof canvas fabric. We are very careful to preserve the integrity of these fabrics and even heat seal the seams. However, the lead free locking zippers are NOT 100% waterproof and even the thread the bags are sewn with can wick moisture if fully soaked for long enough. These bags perform excellently when used with damp items and even when small amount of liquid spill inside. However, if you put your cell phone in it and throw it in the ocean, you will not be happy!