Best thermal wetsuits for swimming in 2025

When temperatures drop in open water, many triathletes will head back to the pool. But that’s a shame, because cold-water swimming has many benefits for our physical and mental health – you just need a good thermal wetsuit for swimming.

Plus, if you can swim through the winter you’ll boost your skills ready for next year’s race season. We won’t sugar-coat it, though, winter swimming is a different beast. It gets cold in there. Very cold!

Expect to do shorter swims and prepare to take care of yourself to avoid cold-water shock, hypothermia and the after-drop. Helpfully though, many brands are now offering thermal-lined swimming wetsuits which make a huge difference.

Here, we test some of the best.

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Best thermal wetsuits for swimming

Orca Openwater RS1 Thermal

• $499 / £369

You’ll notice from the photos that the neckline sits a bit higher on the Orca.

That’s thanks to an inner ‘batwing’ layer of neoprene inside the suit that sits across the back and pulls over your head to add extra protection against trickles through the zip and provide a snug fit to stop water ingress down the neck.

For me, this was a touch of genius as it did make a difference to warmth in the water and, as the neck area is very sensitive to the cold, I welcomed the protection.

Overall this suit became a fast favourite in testing, too. Warmth is provided by a soft-touch ‘X-thermal’ lining which, though warm, didn’t feel restrictive and was easy to pull on.

Orca uses 5mm in the torso to help, too, though more flexible Yamamoto 40 neoprene is used in the arms of the suit, which made for a more natural-feeling swim experience.

Zone3 Thermal Aspect

• £299

In 2021, Zone3 introduced the first breaststroke swimming suit to the market and it’s that which forms the basis of their thermal wetsuit.

As such, it retains a high-stretch nylon panel across the crotch and thighs. Although this allows a good range of leg movement, it did lead to a bit of a chilly area once I entered the water!

The buoyancy levels in the suit are also tailored to the breaststroke position and for winter swimmers who swim breaststroke (or don’t want to swim front crawl in the cold) it’s a great product to have on the market.

Body warmth is added thanks to a ‘Heat-tech’ thermal lining and once swimming, I did find that this kept me much warmer than a standard wetsuit.

One word of warning – this is quite a rigid suit and took a long time to get into, though the fit was good once it was on.

Blueseventy Thermal Reaction

• $699.95 / £550

This is my second thermal Blueseventy suit – my thermal Helix lasted me several cold swim seasons and the Reaction features an upgraded version of the zirconium jersey liner, which has a wool-like feel (leading to this suit being christened the ‘teddy bear’ at home!).

On dry land this felt the thickest suit but it was easy to pull on and that flexibility translated through into my swim with a 4:5:4 buoyancy profile giving a good body position for front crawl. That said, as with my earlier version, I did notice a little more fatigue through my shoulders on longer swims.

Blueseventy markets this suit for swims down to 8°C water, but I found it the warmest on test and the best choice for my chillier swims in waters down to 3°C . From experience, these suits last well, too, so are worth the investment.

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Huub Alta Thermal

• $390 / £285

The Alta is Huub’s entry-level open-water swimming wetsuit and this new thermal version shares the same 2:4 buoyancy profile, designed to give a good horizontal position for those new to open water.

I found the suit comfortable and easy to swim in, even though I initially thought it’d be bit snug (my pre-production sample was a medium, while the size chart put this UK12 tester in a medium/large).

The suit had plenty of stretch, though, and was easier to get in/out of than the more rigid Zone3, the other suit at a similar price point.

The thermal lining did a great job of keeping me warm while the ‘arms neutral’ design gave good flexibility through the shoulders.

I asked a slimmer swimmer for a second opinion on sizing and she reported feeling warmer than in her normal suit, with no water ingress.

Deboer Women’s Ocean 1.0

• $999.95 $699.96 / £784 £549

If I thought the Zone3 was tricky to get into, I thought again when I tried the Ocean 1.0 – it’s a rigid suit with very tiny, tight cuffs! Once on, it gave a toasty swim experience thanks to a ‘ThermaFur’ lining and close fit.

I found it speedy as well, knocking a minute off my usual 1km time in the lake. I did experience a cold trickle down my neck, though.

Deboer tells us this suit is for use down to 8°C water, or you can add the Polar gloves, booties and hoodie (sold separately) and use it down to 6°C.

I actually managed relatively long swims without the hoodie at 5°C, with the caveat being I’m well-acclimatised to cold water swimming and every swimmer is different.

Finally, though, there is that price tag. Unless you’re seriously into winter marginal gains, it’s pricey!

How we tested

These wetsuit were reviewed by open-water swim coach and 220 Triathlon editor Helen Webster.

She tested all of these wetsuits in British lakes with temperatures ranging from 3°C to 9°C. During her test swims, she also added swimming loves and swimming socks, plus a neoprene cap.

These thermal wetsuits have been rated based on criteria that includes warmth, comfort, flexibility, fit (so there’s not regular water ingress), durability, value and ease of pulling on or off.

A rating of 90% and above represents a market-leading product, while 80-90% also comes highly recommended.

Scores between 70-80% mean the product is good, but not perfect, while below 70% means there are some significant flaws.

A quality thermal wetsuit can make braving colder conditions that little bit easier. If you’re looking to keep training consistently, it may also be a good idea to look into our list of the best swim robes to keep you warm and dry.

For more details, read how we test and rate products.

Key features to look for in a thermal wetsuit

Neoprene thickness: The thickness of the neoprene determines warmth and buoyancy in the water, but also walks a fine line between that and being too rigid. Thickness determines warmth; choose based on water temperature (e.g., 3/2mm for mild waters, 5/4mm+ for cold conditions).

Neoprene material: Standard neoprene is warm but less flexible, while super stretch and Yamamoto/limestone neoprene offer better flexibility and insulation.

Thermal lining: Key in a thermal wetsuit. Fleece, thermal or quick-dry linings enhance warmth and reduce drying time.

Seams and stitching: Flatlock for warm water, glued and blind-stitched (GBS) for better insulation, and taped/liquid-sealed for maximum warmth.

Zipper: Triathlon wetsuits normally have a back zip for easy removal. It can be zippered from top up, or bottom down, the latter likely needing help to get into.

Fit: It’s important that a thermal wetsuit is well-fitting. It should be snug but not restrictive, with good seals at wrists, ankles, and the neck to prevent cold water entry.

Hooded options: Essential for very cold waters to prevent heat loss from the head, you can get separate hood, caps, and bands for cold water too.