Speedo Biofuse Protective Cap Size Guide

The Speedo Biofuse Protective Cap is an extra-large capacity swimming cap designed specifically to accommodate high-volume hair. Made from soft and stretchy Elastomeric silicone for maximum comfort, it features a textured interior for grip and a secure fit, and is easy to put on and take off. It helps protect hair against chlorine while creating a smoother profile in the water.

Unlike traditional swim caps, the Biofuse Protective Cap is sized by volume capacity rather than head circumference — choose your size based on your hair type and volume using the guide below.

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Sizing Guide — Speedo Biofuse Protective Cap
Size Volume Capacity Best For
Large (L) 94% more volume than a standard Speedo Silicone Moulded Cap Long hair, braids, or moderately thick / high-volume hair
Extra Large (XL) 154% more volume than a standard Speedo Silicone Moulded Cap Exceptionally thick hair, long extensions, locs, or very high-volume hair

Sizing is based on hair volume, not head circumference. If you are unsure between L and XL, XL is the more generous option and is easier to put on with thicker hair. Contact Allens if you need guidance.

Fit Notes — Speedo Biofuse Protective Cap
  • This cap is sized by hair volume, not head circumference. Do not select a size based on your head measurement — choose based on the amount of hair you need to fit inside the cap.
  • Large (L) provides 94% more internal volume than Speedo's standard Silicone Moulded Cap and is suited to long hair, braids, and moderately thick or high-volume hair.
  • Extra Large (XL) provides 154% more internal volume and is suited to exceptionally thick hair, long extensions, locs, or very high-volume hair.
  • The Elastomeric silicone is softer and stretchier than standard silicone, making the cap easier to put on and take off with large amounts of hair without risking tearing.
  • The textured interior grips the hair to keep the cap securely in place throughout your swim, reducing the likelihood of the cap slipping or lifting at the edges.
  • If unsure between L and XL, choose XL — a more generous cap is easier to put on and more comfortable to wear than one that is too tight for your hair volume.
  • Rinse in cold fresh water after every use. Store flat away from direct sunlight. Do not fold or compress the cap during storage.
  • Unsure? Contact our team or call +44 1827 330600.
Frequently Asked Questions — Speedo Biofuse Protective Cap

Choose based on your hair type and volume, not your head size. Large is suited to long hair, braids, and moderately thick or high-volume hair. Extra Large is suited to exceptionally thick hair, long extensions, locs, or very high-volume hair. If you are unsure, choose XL — it is easier to put on with a lot of hair and more comfortable to wear.

No. The Biofuse Protective Cap is sized by internal volume capacity, not head circumference. Both sizes are designed to fit a wide range of adult head sizes — the difference between L and XL is how much hair they can accommodate, not the size of the head wearing them. Select your size based on your hair volume using the guide above.

Elastomeric silicone is a softer, more flexible variant of silicone used in the Biofuse Protective Cap. Compared to standard silicone, it stretches more easily and returns to its shape more gently, making the cap significantly easier to put on and take off when managing large volumes of hair. It is also more comfortable against the scalp for extended wear.

Yes. The Biofuse Protective Cap is designed to help protect hair against chlorine damage during swimming. While no swim cap is completely waterproof, the silicone construction significantly reduces the amount of chlorinated water that reaches the hair compared to swimming without a cap.

The textured interior surface grips the hair to keep the cap securely in position during swimming. This reduces slipping and lifting at the edges, which is a common issue with high-volume hair where there is more internal movement. It also makes the cap easier to position correctly before pushing off from the wall.

Rinse in cold fresh water after every use to remove chlorine and salt. Allow to dry naturally away from direct sunlight. Store flat — do not fold, roll, or compress the cap. Avoid contact with sunscreen, oils, or petroleum-based products as these can degrade the Elastomeric silicone over time.