Our swim diapers are One Size and fits most babies 8-35 pounds. The general function of a swim diaper is to keep feces and infection-causing germs from leaking into the pool. Our swim diapers do not absorb water like disposable or even cloth diapers and therefore do not add additional weight.
Swim diapers should hold in solid feces, but they are not leak proof. Chlorine in the pool combats any urine that may leak into the pool. However, with that said, it is advised to change your child FREQUENTLY when swimming. And remember, you will need to put a clean swim diaper on each time. The swim diaper of an exclusively breastfed baby should be very snug around the legs.
Keep in mind that most pools have specific rules regarding the use of swim diapers. You should always confirm the rules before entering the pool. Few pools allow regular disposable or regular cloth diapers. Most recommend swim diapers.