How thick should my triathlon wetsuit be?

A triathlon wetsuit is a key piece of swim kit and can significantly benefit performance, comfort, and safety during training and racing.

It’s important to choose a wetsuit with the right thickness for your conditions and preferences since this will affect your buoyancy, flexibility, and comfort as you swim.

Wetsuit construction is somewhat of an art, with neoprene (wetsuit material) thickness varying for each limb, with the aim to raise the swimmer into a hydrodynamic swim position in the water.

Here’s a guide to help you decide the optimal set-up for your triathlon wetsuit.

Understanding wetsuit thickness

Typically measured in millimetres, a wetsuit’s thickness will typically vary between the torso, legs, and arms. If you’ve ever seen a wetsuit described as 5/4/3mm, this refers to the thickness at the core/legs/arms.

Wetsuits are thickest at the core, this is both because the trunk can be the heaviest part of the body and due to internal organs requiring the most insulation against the effects of cold water.

Mild climate or short distances

In warm water of 20°C and above, you’ll either want to forego the wetsuit altogether for sprint distances, or choose a sleeveless or thin 2mm suit. This will provide a hint of buoyancy and protection, while remaining incredibly flexible for fast swimming.

Colder temperatures or middle-long distances

Moderate climes of 10 – 19°C necessitate a wetsuit of at least 3mm/2mm thickness. If you want a suit that can cope with both moderate and colder water, or suffer from the cold more easily, then look for a suit with a 4mm or 5mm neoprene thickness.

Cold water swimming

Any water below 10°C will require a thermal triathlon wetsuit to protect your body against the dangers of cold exposure, primarily hypothermia. For this, look for a suit and cold water swim gear with thermal lining and a neoprene thickness of at least 4-5mm. Just bear in mind that anything above 5mm is not permissible for triathlon racing.

Triathlon race regulations

It’s absolutely fine to don a wetsuit of any thickness when you’re training. If you swim in particularly cold temperatures, then you’ll likely prefer a thickness of over 5mm neoprene to keep you toasty.

There are however specific rules when it comes to race conditions, with World Triathlon stipulating a maximum wetsuit thickness of 5mm for competitions. Ensure your wetsuit complies with your race regulations to avoid disqualification.

When it comes to triathlon racing, wetsuits are allowed to be worn when swimming in water up to 24.5°C and they are mandatory in water below 16°C.

Wetsuit fit and comfort

Though a – the thicker, the better – attitude may be tempting to entice into the cold depths during training, it’s worth noting that thicker wetsuits can restrict movement and cause discomfort. It’s for this reason that wetsuit brands employ Yamamoto neoprene to aid with flexibility over key areas like over the rotator cuffs and elbows.

Fit is king when choosing the right wetsuit. Consider a thinner suit for short-distance events to allow for maximum freedom of movement, then level up a millimetre as the distance climbs or for colder water temps.

What is Yamamoto neoprene?

The all-conquering Yamamoto neoprene comes in different levels of flexibility, with 38, 39 and 40 cell the most commonly used. The #40 cell is the most flexible and often appears around the shoulders in high-end suits, with 39 cell placed elsewhere. Entry to mid-level suits are more likely to spec a mix of 38 and 39 cell, with the latter being a significant upgrade to the former. The 40 cell is more stretchy and will offer minor advantages to fast swimmers, but if you’re on any type of budget then 39 cell will suffice.

Those with a swim background may want to choose suits that support their technique, so if you have a six-beat kick then there’s little need to use a very high buoyancy suit. Orca’s Alpha, the Sailfish G-Range and Huub’s 4:4 (balanced buoyancy) options are examples of suits made for swimmers who aren’t prone to sinky legs. Many brands will use technology such as Aerodome, a sandwiching of two layers of neoprene with air pockets in the middle, to provide extra lift. If you’re after high levels of buoyancy to support a weak-to-improving leg kick and body position, look out for tech such as Aerodome.

While you may get the best deals online, taking a suit out for a test swim before buying could pay you back in dividends. Size guides vary from brand to brand, and although minor fitting differences might not affect the performance too much (unless it’s way too big for you and water is leaking in), it could make a big difference in comfort. A chafing neck from the outset is the last thing you want in a 3.8km Iron-distance swim, so it’s imperative to make sure you’re well accustomed with your suit before racing in it.

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