Swim Caps: Sizing, Materials and Hair

A swim cap does three useful things: it keeps hair out of your face and off a goggle strap, it cuts drag, and it keeps the head a little warmer. The thing most people buy one for — keeping hair dry — is the one thing no cap does well. Water gets in around the hairline on every cap ever made.

Once you accept that, the decision gets simple. Choose the material for comfort and durability, and choose the shape for the amount of hair you need to fit inside it. Those are the only two variables that matter, and getting the second one wrong is why so many caps end up unused in a drawer.

For children there is a third factor: sizing. Most junior caps are genuinely junior-sized, but the range from four-year-old to twelve-year-old is wide, and a cap that rides up is a cap that gets left at home.

The three materials, and who each one suits

Silicone is the default for almost everyone. It is thick, does not pull hair, tolerates chlorine, and lasts a season or more. It is warmer than the alternatives, which is welcome in a lake and less so in a heated pool. Nearly every cap we recommend is silicone.

Latex is thin, tight, cheap and the lowest drag of the three, which is why competitive swimmers still wear it. It also pulls hair noticeably going on and off, tears easily, and is off the table for anyone with a latex allergy. Buy it for speed or price, never for comfort — and not for a child.

Lycra is a fabric cap. It is by far the most comfortable, fits long hair without a special shape, and gives the scalp some sun protection. It also lets water straight through, so it keeps hair contained rather than dry. If someone has rejected silicone as too tight, lycra is the answer.

Sizing, and how to measure

Measure head circumference with a soft tape around the widest part of the skull, just above the ears and across the middle of the forehead. Junior caps generally cover roughly 19 to 21 inches and adult caps roughly 21 to 23. Above that you want a cap explicitly sold as large or extra large, which exist mainly to accommodate hair volume rather than skull size.

If the cap is right and it still rolls up off the back of the head, the problem is usually hair being forced into a crown with no room for it. That pushes the cap forward and up. A long-hair or high-volume cap fixes it; a tighter standard cap does not. Our sizing guide has the full table.

Caps, ears and hair damage

A cap is not ear protection. It covers the outer ear but does not seal the ear canal, so it does very little to prevent water entering — and water sitting in the canal is what leads to swimmer's ear. If ear infections are the concern, the tool is a pre-molded ear plug, optionally held in place under a cap.

On hair damage, a cap helps but does not solve it. It reduces how much chlorinated water reaches the hair, which is worth having. Rinsing hair in fresh water before swimming so it absorbs clean water first, and rinsing again immediately afterwards, does more than any cap. For textured or protectively styled hair, a high-volume cap that does not compress the style is the single biggest reduction in breakage available.