I was at my local pool last Tuesday and watched a woman spend the first five minutes of her swim just adjusting her suit. Pulling the back down. Hiking the straps up. Every time she pushed off the wall she had to tug the leg line back into place. In thirty minutes she maybe swam 200 metres. The rest was fidgeting.

The thing is, she wasn't wearing the wrong size. I'd put money on that. Her suit fit her fine. It fit her perfectly, actually — for standing still. And that right there is the problem that nobody really talks about.

Swimwear has one of the highest return rates in fashion, somewhere between 30 and 40 percent depending on who you ask. Four out of every ten suits get sent back and fit is the reason almost every time. But what gets me is that most of these women tried the suit on. They checked the mirror. They did the turn. They thought yeah, this looks good. Then they got in the water and the fit isn't great.

The mirror lied to them. That is what happened.

I have read so many swimsuit fit guides at this point and they all start in the same place. Stand in front of the mirror. Check the straps. Look at the shape of the suit on your body. Some of them get really into it and sort you by body shape — Pear, Hourglass, Rectangle — then tell you which styles will "balance your proportions" or "create the illusion of curves."

Which is fine advice. For a photoshoot.

But if you actually get in the water, if you swim laps or paddle out past the break or spend your Saturday mornings doing 2K in the ocean with your swimming club, that kind of advice is not going to help you. A suit that looks great in photos and a suit that actually works in water are two completely different things. The distance between those two things is where all those returns come from.

What you really need to know is how the suit behaves when it gets wet. When your arms are moving. When you are kicking. When waves are pulling at the fabric. That is fit. Everything else is just how it looks on dry land.

I have landed on four tests over the years that are much better at predicting how a suit will actually perform than any mirror check. You can do most of them in a changing room. If the shop has a pool or you can talk them into letting you do a dunk test, even better because fabric behaves differently when it is wet and that difference really matters.

• The overhead reach. Stand with your arms down at your sides then sweep both arms all the way up like you are catching at the top of a freestyle stroke. Hold it there for a few seconds and pay attention to what happens. If the neckline drops or the back of the suit rides up or the leg openings shift around, you have a torso-length problem. And that is not a small thing. Every single stroke you take in the water puts that same load on the suit. A little pull on rep one becomes a real problem by rep five hundred.
• The squat and stand. Drop into a full squat, as deep as you can go in the changing room, then stand back up. The bottoms should be exactly where they started. No riding up between your legs, no pulling at the waist, no bunching at the hips. If anything moves then the cut does not match your body mechanics. And I want to be really clear about something here. That is not a body problem. That is an engineering problem. Suits that ride up usually have side panels that are too narrow or not enough compression at the hip. It is the suit's fault not yours.
• The twist and reach. Stand with your feet shoulder-width apart. Rotate your torso to one side while reaching the opposite arm across your body. Then do the other side. The suit should twist with you, it should not fight you. If you feel pulling across the chest or tightness through the midsection, the fabric cannot handle rotation-heavy activities like surfing or open water swimming. Lap swimmers can get away with a tighter fit because the movement is mostly in a straight line. But everyone else needs more give than that.
• The entry and exit check. Put the suit on. Take it off. See how long it takes and how much effort you need. This seems like nothing until you are standing in a car park in February with numb fingers and wet skin and a suit that is basically vacuum-sealed to your body. Thicker neoprene suits like springsuits trade easy entry for better thermal performance and that is a fair trade-off. But you should know about it before you buy, not figure it out shivering next to your car.

Here is something that genuinely bothers me about how swimwear gets sold. A woman buys a suit. Fits great. She wears it to the pool three times a week. Six weeks later the suit is sagging through the hips, stretched out across the chest, kind of see-through in places where it definitely was not see-through before. And she thinks to herself, did I buy the wrong size? Has my body changed? Was this just a bad purchase?

Nope. The pool ate her suit.

Chlorine is corrosive. Specifically it is corrosive to elastane which is the stretchy fibre that gives swimwear its snap and its ability to bounce back into shape. Standard nylon-spandex blends, which is what most recreational swimwear is made from, start breaking down within weeks of regular chlorinated use. The chlorine goes after the urethane bonds in the elastane and pulls them apart bit by bit. First the suit gets a little loose. Then you notice these fine sand-like grains appearing on the fabric surface, which is literally the elastane falling apart. Eventually the whole suit goes baggy, the colour fades, and you are back at the shop buying another one.

And the really annoying part is that the damage does not stop when you get out of the pool. Residual chlorine sitting in the fabric keeps eating at those fibres while the suit is hanging in your bathroom. If you are not rinsing it in cold fresh water straight after every swim the whole process speeds up.

So when we talk about fit we also have to talk about materials. A suit built with chlorine-resistant fabrics — polyester blends, PBT constructions, or plant-based alternatives like Yulex natural rubber — will hold its compression and shape and colour for months of daily use. Not weeks. The molecular structures in these materials just do not react with chlorine the same way that elastane does. That is not a marketing line. That is chemistry.

A suit that fits great on day one but falls apart by day forty was never really a good fit. It just had not failed yet.

This is the part where I lose patience with the generic fit guides. They will write a thousand words about scoop necks versus high necks but they will not tell you what construction survives a set of 400-metre repeats versus what holds up during a two-hour paddle session.

Different activities put different demands on a suit. Here is what I have found actually matters.

Lap swimming is probably the hardest thing you can do to a swimsuit. Hundreds of the same arm movements over and over, flip turns slamming fabric against your body, chlorine exposure three to five times a week. What matters here is compression fit, low drag, chlorine resistance, and a racerback or cross-back construction that completely frees up the shoulders. Built-in shelf bra is better than underwire because underwire and pool walls do not get along. And here is one that people get wrong all the time: the suit should feel snug when it is dry. Almost compressive. Water adds slack to everything so a suit that feels "comfortable" on land is going to feel loose in the pool. And loose means drag.

Open water and ocean swimming is a completely different situation. You are dealing with temperature, current, waves, and how visible you are in the water. Bright colours out here are not a fashion choice, they are a safety consideration. Your suit needs full back coverage for warmth and sun protection, secure closures that will not come undone when waves hit you, and the ability to layer underneath a springsuit or steamer when the water drops below 18°C. Wearing a pool suit in the ocean and then wondering why you are freezing after twenty minutes is like wearing trainers to hike a mountain. Technically footwear. Functionally wrong.

Surfing needs suits that can survive wipeouts. That is the starting point, everything else comes after. Pop-up range of motion, quick drying, board-compatible construction — all of that matters but if the suit shifts out of position on your first duck dive then none of it counts for much. Stay away from ties, clasps, or hardware that can catch on boards or leashes. Bonded seams and performance neoprene can handle the kind of forces surfing puts on a suit. Regular fashion swimwear cannot.

Paddleboarding is one that sneaks up on people. You are kneeling, standing, reaching, sometimes falling in, and the whole time you are sitting in direct sun. UV damage is cumulative and UV reflected off the water surface makes the exposure significantly worse. UPF 50+ fabric is not optional for paddleboarding. Sleeveless or short-sleeve cuts give you a good balance of coverage and ventilation, and you want something that works on its own in warm weather and as a base layer under a wetsuit when it gets cooler.

Multi-activity women — and honestly this describes most of the women I know who spend real time around water — need one suit that can handle the pool on Wednesday, the ocean on Saturday, and the paddleboard on Sunday without falling apart. Durable fabric, UV protection, a fit that holds across different movement patterns, and construction that does not degrade from going back and forth between chlorine and saltwater. That is what versatility actually looks like when you live between the pool and the ocean.

One more thing because it comes up constantly and it gets to me every time.

Modern clothing sizes including swimwear go back to measurement systems that were built using body data from men in the military. In the 1940s. Those systems were never meant to represent the range of actual women's bodies and eighty years of trying to patch them has not really fixed the core problem. On top of that, women's bodies change naturally throughout the month because of hormones and fluid retention, which is completely normal but completely ignored by every sizing chart out there. The result is that being "between sizes" is basically the default experience for most women.

If you are between sizes across multiple brands, the sizing system is what is broken. Not you.

Here is the practical fix. In performance swimwear, if you are genuinely stuck between two sizes, go up. A suit that is a little bit loose will compress against your body slightly when it gets wet. A suit that is too tight restricts your breathing, limits your shoulder range, digs at the leg line, and makes every stroke harder than it needs to be. You can swim in slightly loose. You cannot swim in too tight.

The good brands publish height-based sizing alongside bust and hip measurements. Look at that column. For one-piece suits and springsuits especially, torso length is usually the measurement that actually determines whether the suit fits, and it is not the one most people check first.

After all of this — the movement tests, the material science, the activity matching, the sizing frustrations — the real standard for performance swimwear turns out to be pretty simple.

You should not have to think about your suit once you are in the water.

Not adjusting it. Not pulling at it. Not worrying about what moved or what is about to shift. The suit stays where you put it. It moves the way your body moves. It disappears. And all that is left is you and the water.

That is what people mean when they talk about the "second skin" feeling. It is not a marketing phrase. It is an actual physical thing where the suit stops being a barrier and you just feel like you are in the water with nothing in the way. And once you have had that experience, going back to a suit that needs constant managing feels like wearing someone else's clothes.

Test with movement. Choose for your activity. Demand materials that still hold their shape after week six. And the next time a fit guide tells you to stand in front of a mirror and check your silhouette, just keep scrolling.

Your swimwear should be built for what you do in the water. Not for what you look like standing next to it.