Why you need a swim cap for triathlon


It is not always clear if you need a swim cap to do a triathlon. Each event is different. Most will provide you with an official swim cap that is mandatory but some events don’t. But it is not clear whether you should wear your own swim cap anyway. Let’s make sure you know what to do on race day!

Do you need a swim cap for triathlon?

In most triathlons, it is mandatory to wear the official swim cap provided. It is also common to wear your own swim cap under the official one. Therefore you need a swim cap for a triathlon. It is especially good for aerodynamics and safety.

So first, always check the rules of the event you have entered. The race pack might provide you with a swim cap or not. But it will be clearly stipulated if you have to wear one. As you can’t be too careful, I recommend always bringing a swim cap with you to a triathlon. At least you can decide to wear it till the last minute or help a friend out.

Example of an official race swim cap I got in a triathlon

If your event starts in a pool, you definitely need a swim cap. It’s essential to prevent hairs from going into the cleaning filters of the pool. Just wear it!

For open water racing, the most common case, consider you need a swim cap. Let’s look at the reasons you need a swim cap in a triathlon in the next paragraph.

Reasons to use a swim cap in triathlon

  • Safety: be more visible

It’s safer to wear a swim cap, especially a green one or an orange one if you can choose the color. Generally, they are mandatory and provided by the Race Organizers. The color of the cap is used by the organizers to differentiate the different waves of athletes and make you more visible in the water.

Some of my swim caps: see how the RED one will be much more noticeable in the water
  • Be more aero

The main advantage of a swim cap is to reduce the drag from your head. This is even more true for people with lots of hair. It has been demonstrated by science that hydrodynamics is key in swimming. A study(*) looked specifically into the role of the swim cap in drag reduction. They considered a female swimmer with a cap vs no cap and as a result, they demonstrated a 15% reduction of hydrodynamic drag when wearing a swim cap. This is not just a marginal gain, and this is why you should definitely wear a swim cap if you care about not wasting time against others.

You will notice on race day that everyone wears a swim cap; not wearing one will make you at a disadvantage against others.

(*) “The effect of wearing a swim cap on the swimmer passive drag”, Daniel A. Marinho et al., 2011

  • Be even more aero

That’s when wearing two swim caps comes into play. Some studies have found that silicone cap with no seams are the best for aero. So the more the shape of your head is smoothened without any wrinkle the better it is. Generally, the official swim caps are very thin and made of latex and therefore aren’t great to smoothen your head. That’s one of the reasons you can wear a swim cap underneath the official swim cap.

Comparison of thickness between a common silicon cap and a latex swim cap

Using two swim caps is often better to improve aero. You would have two layers of “smoothering” and have the possibility to hide the goggles between the two caps which improves aero as well.

Thus do not hesitate to buy a swim cap for your triathlon, you can find very nice caps on Amazon.

  • Keep long hair in place

There is nothing more annoying when swimming freestyle than having your hair in the way each time you breathe. Of course, people with short hair won’t know this feeling, but wearing a swim cap makes the swim more appreciable for people with long hair.

  • Keep your head warm

Many triathlons start in a river, a lake, or in the sea. This means the water can be quite cold; even during the summer. If that’s the case for your event, consider wearing a swim cap (or two) to keep your head warm. If it is really cold, only a neoprene swim cap can help you keep warm.

  • Keep your hair dry

This is important for people with long hair if the weather is not very warm. Once you come out of the water, you will have to hop on your bike. With wet air, on a windy and cold day, it’s a recipe to catch a cold and struggle to keep warm on the bike.

Why do triathletes wear two caps?

It is common for triathletes to wear two swim caps for better aerodynamics but also to maintain the goggles in position. The goggles are compressed between the two layers of swim caps; with the benefit of the friction of the silicon cap. Also, official swim caps can be very uncomfortable with their latest material.

Have you ever been to a triathlon race start?

It’s a mess! A big mass of people all at once trying to head in the same direction as fast as possible. That’s when things can look a bit like a fight. You can easily get your goggles knocked off by someone passing by or trying to overtake. If that happens, you will have to stop a minute to try to fit them back in place. So not very convenient. The double swim cap solution will prevent you from this happening.

Me wearing two swim caps (the official one in white for women and a black one underneath)

Should goggles go under the swim cap?

It is best to wear your goggles in between two swim caps. If you wish to wear only one cap, you can wear your goggles below the swim cap to prevent them from being knocked off by other swimmers during the rough start of a triathlon.

If you liked this article, do not hesitate to look at my other articles on swimming:

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