KALIBRA KALIBRAAdjustable open heel fin with blade in three materials and the foot pocket in soft thermoplastic rubber. Blade in 3 materials: Structure in Tecnoflex to improve performance and durability. Ribbings in thermoplastic rubber give the blade elasticity and lateral stability. Channels in Cristalflex optimize the channeling of water and fin performance. Sizes: XS - M: from 36 to 41 ML - XL: from 42 to 47