This is a swim diaper and bathing suit in one. Wear it alone or under a swim suit or swim trunks. Do not add anything to the inside; you do not want a swim diaper to be absorbent - it would just absorb pool water and could weigh the child down. The design is based on containment. Make sure it fits snugly without leaving red marks. When you get out of the pool, make sure to put on an absorbent diaper to prevent accidents.