Atomic Aquatics Split Fins 'Smoke on the Water' use a comparably lightweight compound that has high energy characteristics to lower energy use and increase efficiency. The 'Smoke on the Water' is the only version of Atomic split fins to be fitted with their advanced spring straps as standard.   Atomic Aquatics split fins are the perfect balance between a lightweight, soft, short split fin that is easy to kick with but require a lot more kicks to produce the same level of thrust and a stiff compound with a long blade length that far too much effort to produce effective propulsion. Atomic Aquatics have optimised all these variables to produce an easy kicking, high thrust fin that delivers speed and efficiency.   US Men's Shoe Sizes: US5.5 = Small, US6-8.5 = Medium, US9-11 = Large and US11.5-13 = Extra Large US Lady's Shoe Sizes: US6-7 = Small, US8-10 = Medium, US11-12 = Large and US13-14 = Extra Large Also check out  the variety of dive computers we carry visit : https://gs-diving.com/fins/ Also check out Dive Singapore for the variety of gears we carry visit : https://www.divesingapore.sg/product-category/scuba-equipments/