Built-in Ultimate Swim Diaper protects at UPF 50+! . Microfiber shell with built-in Ultimate Swim Diaper. 27 States now require or encourage the use of approved swim diapers for diaper-aged children swimming in public pools. The iplay Ultimate Swim Diaper features a snug-fit around legs and waist to contain any solid matter, a waterproof layer to prevent leakage, an extra-absorbent layer to absorb wetness, and a wick-away liner to pull moisture away from baby's skin. Fits babies 10-18 lbs.