Kiefer Adult Swim Diapers are designed with worry free swimming in mind. These washable and reusable swim diapers are lined with polyester and are stain resistant. They can be worn alone or under other swimsuits. Kiefer Adult Swim Diapers offer a trim fit for free movement and will not absorb water like standard diapers. White. Size XL. Kiefer - The First Name in U.S. Swimming since 1947.