Speedo Fastskin Cap Size Guide

This size guide covers the Speedo Fastskin Racing Cap, available in sizes S, M, and L. The Fastskin Cap features IQfit™ technology developed by Speedo Aqualab using precise global head scanning data, creating a true 3D cap modelled on the real contours of the head and face for optimal hydrodynamic performance and reduced drag. It is World Aquatics approved for use in competition.

To find your correct size, measure the circumference of your head and the ear-to-ear distance over the top of your head using a soft measuring tape. If you have long hair, Speedo recommend wearing the cap alongside the Fastskin Hair Management System (worn underneath the cap) for the best fit and performance.

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How to Measure

Use a soft measuring tape held snugly against the skin. Take both measurements before comparing to the sizing table.

  • A
    Head CircumferenceMeasure around the fullest part of your head, starting at the centre of the forehead, keeping the tape level and horizontal all the way around.
  • B
    Ear to EarMeasure from earlobe to earlobe over the top of the head, keeping the tape flat against the skull.

If your measurements fall between sizes, size up for added comfort — particularly if you have thick or long hair or plan to use the Hair Management System underneath.

Speedo Fastskin Cap
Speedo Fastskin Racing Cap size guide
Sizing Table — Speedo Fastskin Racing Cap
Measurement S — Small M — Medium L — Large
Head Measurements (cm)
A — Head Circumference ~53 cm ~58 cm ~63 cm
B — Ear to Ear (over top) ~33 cm ~38 cm ~43 cm

Measurements are approximate. The Fastskin Cap is made from 100% silicone and has some stretch — if between sizes, size up.

Fit Notes — Speedo Fastskin Racing Cap
  • The Fastskin Cap should feel firm and close-fitting against the head with no air pockets, wrinkles, or gaps — this is essential for optimal hydrodynamic performance.
  • The cap is made from 100% silicone which has some stretch but will feel tighter than a standard training cap. This is normal — the IQfit™ technology is designed to conform to the contours of your head for the best possible seal and drag reduction.
  • When putting on the cap, use both hands to stretch it over the back of the head — avoid pulling from the front edges as this can distort the cap's shape.
  • Take care with fingernails and hair grips when putting on or removing the cap — silicone can tear if snagged.
  • If between sizes, size up — a cap that is too small is harder to put on, more prone to tearing, and will be uncomfortable during a race.
  • Rinse in cold fresh water immediately after every use. Store flat and dry, away from direct sunlight. Do not fold, roll, or compress the cap during storage as this can cause creasing.
  • Do not apply petroleum-based products, sunscreen, or hair products before putting on the cap — these can degrade the silicone.
  • 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 Fastskin Racing Cap

Yes. The Speedo Fastskin Racing Cap is approved by World Aquatics (WA) and is legal for use in all sanctioned competitive swimming events. It meets all international standards for competition use.

IQfit™ is Speedo Aqualab's proprietary cap fitting technology, developed using precise 3D scanning data from swimmers' heads worldwide. The data was used to create a true 3D cap shape modelled on the real contours of the head and face, providing a more secure, anatomical fit than standard swim caps. Testing has shown that the Fastskin Cap can reduce drag force by up to 3.4% compared to a standard cap.

Measure the circumference of your head starting at the centre of the forehead, and your ear-to-ear distance over the top of the head. Compare both measurements to the sizing table above. If your measurements fall between sizes, choose the larger size — a cap that is too small is harder to put on, more prone to tearing, and uncomfortable during competition.

The Speedo Fastskin Cap is designed for hydrodynamic performance, not as a waterproofing device. While it significantly reduces water penetration compared to a standard cap, it is not completely waterproof. Water will still enter around the edges and through the hair during swimming.

Hold the Fastskin Cap at the sides with both hands, place it at the front of your forehead, and stretch it back over the top and down the back of the head in one smooth motion. Avoid pulling the cap from the front edges as this can distort its shape. Check that there are no air pockets and that the cap sits flat all the way around.

The Fastskin Cap is a competition racing cap and while it can be used for training, regular training use will shorten its lifespan. The silicone is durable but benefits from being reserved for races and competition warm-ups. For everyday training, a standard silicone or latex cap is recommended. Speedo offer a wide range of training caps at Allens.

Rinse the cap thoroughly in cold fresh water immediately after every use to remove chlorine, salt, and any residue. Allow to dry completely before storing. Store the cap flat, away from direct sunlight and heat. Do not fold, roll, or compress the cap as this can cause creasing that affects its shape and fit. Avoid contact with petroleum-based products, sunscreen, or hair products as these can degrade the silicone.

The Fastskin Cap is designed to fit snugly to achieve the IQfit™ seal and maximise hydrodynamic performance — it will feel tighter than a standard training cap. This is normal and intentional. The silicone will ease slightly with regular use. If the cap feels painfully tight or leaves deep marks after a short time in the water, you may need to size up. Speak to a member of staff at Allens if you are unsure.