Speedo Biofuse Training Fin Size Guide

The Speedo Biofuse Training Fin is a 100% silicone training fin designed to add speed and power to your pool workout. Wear them during technique drills for easy speed, or use them to work harder and challenge your lower body with added water resistance. The extra propulsion helps develop ankle mobility whilst the resistance builds strength and endurance. Available in six sizes covering UK shoe sizes 2–12.

Select your size using your UK shoe size in the table below. Where your shoe size falls at the boundary between two sizes, we recommend sizing up for a more comfortable fit.

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⚡ Speed & Power Adds extra propulsion to your stroke, giving you easy speed during technique drills and increased power during strength sets.
🦶 Ankle Mobility The extra propulsion and resistance of the fin encourages better ankle extension, helping to develop flexibility over time.
💪 Strength & Endurance Added water resistance challenges the lower body, improving leg strength and cardiovascular endurance with every session.
✅ 100% Silicone Made from 100% silicone for a soft, comfortable foot pocket that is durable, chlorine resistant and easy to put on and take off.
Sizing Table — Speedo Biofuse Training Fin
Size UK Shoe Size EU Shoe Size US Shoe Size
XS 2–3 35–36 3–4
S 4–5 37–38 5–6
M 6–7 39–41 7–8
L 8–9 42–43 9–10
XL 10–11 44–46 11–12
XXL 11–12 47–48 12–13

Sizing is based on UK shoe size. Where your shoe size falls at the boundary between two sizes, we recommend sizing up for a more comfortable fit.

Fit & Usage Notes — Speedo Biofuse Training Fin
  • Select your size using your UK shoe size. If you are between sizes, size up for a more comfortable fit — fins that are too tight can cause discomfort and cramping during longer training sets.
  • The 100% silicone foot pocket is soft and flexible, making the Biofuse Training Fin easy to put on and take off compared to rubber fins. The fit will feel comfortable both wet and dry.
  • Use the Biofuse Training Fin during technique drills to benefit from the added propulsion and focus on stroke mechanics without having to work as hard on propulsion — ideal for front crawl, backstroke, and butterfly kick work.
  • Use them during strength and endurance sets to add resistance and challenge your lower body — the additional workload will build leg strength and cardiovascular fitness over time.
  • The Biofuse Training Fin is suitable for use in front crawl, backstroke, and butterfly kick sets and drills. Not recommended for breaststroke due to the outward kick motion.
  • If you are new to fin training, introduce them gradually — start with shorter sets and build up duration as your legs adapt to the additional resistance and ankle extension required.
  • Always rinse in fresh water after every use and allow to dry naturally away from direct sunlight. Store flat in a cool, dry place — do not fold or crush the blades.
  • Unsure? Contact our team or call +44 1827 330600. Speak to a member of staff at Allens if you are unsure.
Frequently Asked Questions — Speedo Biofuse Training Fin

Select your Biofuse Training Fin size using your UK shoe size and the sizing table above. The fins are available in XS to XXL, covering UK shoe sizes 2 to 12. If your shoe size falls at the boundary between two sizes, we recommend sizing up for a more comfortable fit. Speak to a member of staff at Allens if you are unsure.

The Speedo Biofuse Training Fin is a silicone training fin designed for speed, technique work, and developing ankle mobility, with a blade profile suited to general training use. The Biofuse Fitness Fin has shorter, stiffer blades specifically designed to create maximum resistance, prioritising strength and cardiovascular development. The right choice depends on your training goals — if you want to focus on technique and ankle mobility, choose the Biofuse Training Fin; if you want to maximise leg workload and resistance, choose the Biofuse Fitness Fin.

Yes. The Biofuse Training Fin is suitable for swimmers of all levels. If you are new to fin training, introduce them gradually — start with shorter sets and build up over time as your legs and ankles adapt. The 100% silicone foot pocket makes them comfortable and straightforward to use, and the added propulsion can be particularly helpful for beginners working on body position and kick technique.

Yes. The propulsion created by the fin blade encourages greater ankle extension during the kick cycle, which over time helps to develop ankle flexibility and mobility. This is particularly beneficial for swimmers whose ankle stiffness limits their kick effectiveness. Regular fin use as part of a structured training programme can contribute to improved ankle mobility alongside other flexibility work.

The Speedo Biofuse Training Fin is suitable for front crawl, backstroke, and butterfly kick sets and drills. They are not recommended for breaststroke, as the outward whip kick motion is not suited to standard fin design. They are particularly effective for front crawl kick sets, body position drills, and rotation work.

Silicone fins like the Speedo Biofuse Training Fin are generally softer and more flexible than rubber fins, making them easier to put on and take off and more comfortable to wear during extended training sets. Silicone is also highly chlorine resistant and durable, maintaining its properties over time with proper care. Rubber fins can be stiffer and harder wearing but may cause more friction and discomfort around the foot pocket during longer sessions.

The Biofuse Training Fin is designed for pool use. While they can be used in open water, they are optimised for pool training drills rather than open water propulsion. Always rinse thoroughly in fresh water after any use in the sea or open water to remove salt and debris, which can degrade the silicone over time.

Rinse your Biofuse Training Fins in cold fresh water after every use to remove chlorine, salt, and debris. Allow them to dry naturally away from direct sunlight and heat sources — prolonged UV exposure and high temperatures can degrade the silicone over time. Store them flat or hanging in a cool, dry place. Do not fold or crush the blades during storage as this can cause permanent deformation.