The short answer
Two things decide whether a girls’ swimsuit is a good buy, and neither of them is the print. The first is torso length, which almost nobody measures and which is the reason a correctly sized suit still drags at the shoulders. The second is the fibre, because polyester-based swim fabric survives chlorine and nylon-based fabric does not.
| Style | Best for | Weakness |
|---|---|---|
| One-piece | Swim lessons, beach, anything active | Sized by torso length as much as by chest. Gets this wrong and nothing else helps |
| Long-sleeve rash suit | Long sun exposure, snorkelling, all-day beach | Slower to dry, colder when wet in wind |
| Two-piece (tankini) | Toilet trips, older children who want independence | Rides up in surf. The gap at the back is where sunburn happens |
| Swim dress or skirted suit | Children who want more coverage | Drag in the water. Fine for the beach, poor for lessons |
| Bikini | Paddling, shallow pools, short sessions | Least coverage, most adjusting, most likely to be lost in surf |
If you buy one, buy a one-piece in a polyester-based fabric, in her correct torso length. That covers lessons, beach and holiday, and it will still be intact at the end of a term of swimming.
Torso length: the measurement nobody takes
This is the single most useful thing in this article.
A one-piece swimsuit is a closed loop. It has to go over the shoulder, down the front, under, and back up, and that loop has a fixed length. If a child’s torso is longer than the loop the suit is built for, the suit does not stretch to accommodate her — it pulls the shoulders down. The straps slip, the neckline gapes, and she spends the day hitching it up.
What makes it confusing is that the suit is the right chest size. Every other measurement checks out. So the conclusion people reach is that the brand runs small, or that their child is difficult about swimwear, and neither is true.
How to measure it, in twenty seconds. Run a tape from the top of one shoulder, straight down the front, between the legs, and up the back to the same shoulder. That number is the torso measurement, and it is what a one-piece has to accommodate.
What to do with it:
- If the number is long for her age, go up a size in one-pieces even when the chest fits, or buy two-pieces and rash suits instead, which have no loop to run short.
- If it is short for her age, the usual size will bag at the front, and a two-piece or a suit with adjustable straps is the easier answer.
- Re-measure each season. Torso length grows unevenly with height, particularly between six and ten.
Brands do not publish this, mostly. Where a brand publishes only a body chart and not a garment chart, this is one of the numbers worth asking customer service for, and why that distinction matters so much is in why “true to size” means nothing.
The other three places to check the fit
- Shoulder straps. Slide two fingers under a strap and lift. If it lifts more than about two centimetres off the shoulder, it will slip in the water. If you cannot get a finger under, it will mark.
- Leg openings. They should sit flat without cutting in. Red marks after ten minutes on land mean an hour in the water will be miserable. Gaping means sand and pool water flushing through all day.
- The front, when she bends. Ask her to touch her toes. A neckline that gapes standing still becomes a problem swimming, and a suit that rides up at the back when she bends will do it constantly.
Do all three in the shop or before you remove the hygiene strip. Swimwear is the category where returns are most restricted, so the check has to happen before the first wear rather than after.
Fabric: the part that decides whether it survives the term
Swim fabric is a blend of a main fibre and an elastic fibre, and the main fibre decides how it handles chlorine.
| Fabric | Feel | Chlorine | Right for |
|---|---|---|---|
| Polyester, or polyester with PBT | Slightly firmer, matte | Holds up well. The reason competitive training suits use it | Weekly lessons, pool holidays, anything repeated |
| Nylon with elastane | Softer, smoother, brighter prints | Degrades noticeably faster. Loses shape, goes see-through at the seat | Beach and occasional use |
| Recycled polyamide | Like nylon, because it is nylon | Same behaviour as nylon. Recycled is an environmental claim, not a durability one | Same as nylon |
The practical rule: if she swims weekly in a chlorinated pool, buy polyester-based and accept a slightly firmer handle. If it is two weeks of beach a year, nylon is fine and will feel nicer.
Two things people get wrong here. Recycled content says nothing about how long the suit lasts. And “chlorine resistant” on a label is not a regulated term, so it is worth reading the fibre content rather than the marketing line.
What actually destroys a swimsuit
In order of how much damage each does, which is not the order people assume.
- Chlorine left on the fabric. The single biggest factor, and the easiest to fix. Rinse in cold fresh water immediately, before it dries.
- Heat. A tumble dryer or a radiator kills elastane fast. Dry flat, in shade.
- Sun on a wet suit. Drying in direct sun degrades both the elastane and the colour. Shade dries almost as fast.
- Rough surfaces. Pool edges, rocks and slide surfaces abrade the seat. This is why the seat wears out first on a child who sits on the pool edge.
- Being stored wet. A suit balled up in a bag for two days is a suit with a smell you will not remove.
The routine that works takes a minute: rinse cold, squeeze without wringing, dry flat in shade, and alternate two suits so neither is worn damp. Two suits alternated last more than twice as long as one suit worn continuously.
How swim fabric fails, and what a season does to it, is covered further in matching family swimwear.
Choosing by what she is actually doing
| Activity | Buy | Avoid |
|---|---|---|
| Weekly swim lessons | Polyester one-piece, close fit, no skirt or frills | Anything with drag: skirts, ruffles, loose ties |
| All-day beach | Long-sleeve rash suit, or one-piece plus rash top | Bikinis, which mean constant sunscreen on the trunk |
| Pool holiday | Two polyester one-pieces, alternated | One expensive suit worn every day |
| Paddling pool at home | Anything she likes | Overthinking it |
| Water park | One-piece, nothing loose, no ties | Two-pieces and anything that can be pulled off by a flume |
| School swimming gala | Check the school’s rules first | Assuming. Many specify plain and one-piece |
The water park row is a real safety point rather than a style preference, and the reasons are in what to wear to a water park.
Sun protection, and what a UPF label does and does not mean
A swimsuit only protects what it covers, which sounds obvious and is routinely forgotten when a UPF number is on the tag.
A rated garment is genuinely useful for the fabric area. It does not cover the shoulders in a strappy cut, the tops of the feet, the ears, or the parting in her hair. And a rating is tested on new, dry, unstretched fabric, so a stretched wet suit on a growing child is not the tested condition.
What the rating measures, which of the four standards it was tested under, and where the gaps are is set out in UPF 50 swimwear for kids. For the whole-day version, including what goes over the suit, see girls’ beach outfits.
What to skip
- Ties at the neck. Cords at the neck are restricted on children’s clothing for strangulation reasons, and a wet knot is impossible for a child to undo.
- Heavy embellishment. Sequins and appliqués come off in water, and anything that detaches on a small child is a choking hazard.
- Anything that needs adjusting. A suit she has to keep pulling into place will be worn with a towel over it.
- Buying a size up. Loose swimwear drags, rides up and stops covering what you bought it to cover. Buy the size that fits now.
- White. It goes transparent wet, and it is the fabric colour that shows chlorine damage first.
How many, and how long they last
Two suits alternated, replaced when the elastane goes rather than when she outgrows them. The failure signs are specific: the fabric goes slightly transparent at the seat, the leg openings stop lying flat, and the straps no longer recover when pulled.
A polyester suit swum in weekly will usually see out a school year. A nylon suit in the same use often will not, which is the whole argument for the firmer fabric.
Growth is the other clock, and for once it is slower than the wear. Between about five and nine most children hold a swimsuit size longer than they hold a clothing size, because the fabric stretches. The size arithmetic is in clothing sizes by age and weight. Our range is in girls’ swimsuits.
What this guide does not claim
The chlorine comparison between polyester-based and nylon-based swim fabric is directional and well established in swimwear, but the specific hour figures that circulate online come from fabric sellers rather than from independent testing, so we have not quoted them. Treat it as which fabric to prefer, not as a number.
“Chlorine resistant” is not a regulated term. We describe fibre behaviour rather than endorsing any label claim, including our own.
No garment is water safety equipment. Supervision prevents drowning, swim aids are not safety devices, and nothing in this article changes that.
We sell girls’ swimwear. The advice here is to buy two rather than several, to buy the size that fits now, and to prefer a fabric that lasts longer, none of which maximises what you spend.
Frequently asked questions
How do I choose a girls’ swimsuit? Measure her torso length, check the straps and leg openings, and pick a polyester-based fabric if she swims in a chlorinated pool weekly. The print is the last decision, not the first.
What is torso length and why does it matter? It is the loop from shoulder, down the front, under and back up. A one-piece has a fixed loop, so a long torso pulls the shoulders down even when the chest size is right.
How do I measure it? Run a tape from the top of one shoulder, down the front, between the legs and back up to the same shoulder.
Why do the straps keep slipping? Almost always torso length rather than strap design. The suit is being pulled down because the loop is short for her.
One-piece or two-piece? One-piece for lessons and anything active. Two-piece for independence at the toilet and for older children who prefer it, accepting that it rides up in surf.
Which fabric lasts longest in a pool? Polyester-based, including polyester with PBT. Nylon with elastane feels softer and degrades noticeably faster in chlorine.
Does recycled fabric last as long? Recycled polyamide is still nylon and behaves like nylon. Recycled content is an environmental claim, not a durability one.
Is “chlorine resistant” on the label meaningful? Not as a regulated term. Read the fibre content instead of the marketing line.
What destroys a swimsuit fastest? Chlorine left on the fabric, then heat. Rinse in cold fresh water before it dries and never tumble dry.
Should I buy a size up so it lasts? No. Loose swimwear drags, rides up and stops covering what you bought it for.
How many swimsuits does she need? Two, alternated. Two suits last more than twice as long as one worn continuously.
How do I know when to replace it? The fabric goes slightly transparent at the seat, the leg openings stop lying flat, and the straps no longer recover when pulled.
Does a UPF swimsuit mean she does not need sunscreen? Only for the area it covers. Shoulders in a strappy cut, feet, ears and the hair parting still need cream.
What should I avoid on a girls’ swimsuit? Ties at the neck, heavy sequins or appliqués, white fabric, and anything that needs constant adjusting.
Why does she refuse to take the towel off? Usually because she did not choose the suit, or she wants more coverage than it gives. Both are solved by asking rather than insisting.
About this article
Written and fact-checked by the PatPat Editorial Team. How we research, source and review what we publish is set out on our editorial standards page.
Method. No swimsuits were laboratory-tested for this article and no products are ranked. The fabric comparison is described directionally, and where widely circulated figures come from sellers rather than independent testing we have said so rather than quoting them.
Sources. UV and what the index means for a child: US EPA, UV Index Scale. Supervision and water safety: American Red Cross, swim safety. Cords on children’s clothing: CPSC guidance on drawstrings.
Related. The whole beach-day outfit around the suit is in girls’ beach outfits; what a UPF rating measures is in UPF 50 swimwear for kids; and babies and toddlers are covered in the baby swimwear guide.
Last updated 17 September 2026 · Next review September 2027
