A unique one-piece fin design with ankle strap for improved comfort and fit. Unlike many of the other swimming fins on the market, the Zone3 fins feature an ankle strap rather than a full fitted heel which allows a better fit, less chafing and unrestricted ankle movement. Using fins as part of your swim training can have huge benefits to your overall swim efficiency and speed. Many developing swimmers underestimate how important the kick is to the overall body position and speed through the water. Swimming with fins can significantly help improve ankle flexibility which is vital in creating a fluid leg kick. By using these fins as part of your kick and swim sets you will automatically get the feeling of how your feet should be positioned when swimming unassisted and over time your ankle flexibility and leg strength will improve. Size Guide: Extra Small - UK 3.5-5 / EU 36-38 Small          - UK 5-6.5 / EU 38-40 Medium     - UK 6.5-9 / EU 40-43 Large         - UK 9-11  / EU 43-45 Extra Large- UK 11-13/ EU 45-47