Sea swimmers tend to assume they are getting away with something, and pool swimmers tend to suspect they are paying for it. Both are roughly right, though rarely for the reasons given. Chlorine and salt water are each hard on a swimsuit, but they attack it in entirely different ways, and the honest answer to which is worse depends on whether you are asking about the elastane or the garment as a whole.
The verdict first: a chlorinated pool is harder on the fibre that makes a swimsuit work, and nothing about a sea swim comes close to that kind of damage. The sea, though, arrives with conditions the pool does not — abrasive grit, a long dry in direct sun, heat on bare fabric — and those account for much of what people call a suit wearing out. One ruins the elastic. The other wears out everything around it.
Chlorine attacks the fibre itself
Chlorine is an oxidiser, and it works for the entire time your suit is in the water. It breaks down the soft segments inside elastane, the part responsible for stretching and springing back, and that breakage is permanent — no rinse, wash or rest day reverses it. A pool is commonly held at one to three parts per million of free chlorine, which is trivial for a single swim. The problem is cumulative: a suit worn three times a week in a lane pool can lose its hold inside a season while still looking respectable on the hanger. Warm water accelerates the same reaction, which is why heated indoor pools are harder again.
Salt does its damage mechanically
Salt does not oxidise elastane. Dilute seawater is, chemically, close to the mildest water your suit will ever sit in, and that is why sea swimmers get away with more. Its damage is physical instead. As the suit dries, dissolved salt returns to hard crystals inside the knit, lodged between yarns that are then stretched, folded and walked home in. That is abrasion, and it concentrates where tension is highest: leg openings, straps, the seat. Sand compounds it, because a knit holds fine grit far more willingly than it releases it, and a gritty seam grinds with every movement. Salt is hygroscopic too, so an unrinsed suit draws moisture from the air and dries far more slowly.
What the beach adds and the pool does not
The sea is rarely the whole story of a beach day. A suit taken to the coast typically spends six or eight hours in open sun, much of it drying on the body, and ultraviolet light degrades nylon and elastane and strips dye at the same time. Light reflected off water and pale sand raises the dose, and fabric drying in full sun gets hot in its own right. The same suit at a pool usually gets a shorter, shadier day, and at an indoor pool none of this at all. The result is an inversion: the gentlest water comes packaged with the harshest light, while the harshest water sometimes comes with no light whatsoever.
Chlorine wears out the elastic. Salt, sand and sun wear out everything around it — and the second kind is what people mistake for a cheap suit.
The honest ranking
If you want an order, by how quickly each shortens a suit's life: a hot tub first and by a wide margin, since it combines heat, concentrated sanitiser and a long motionless soak. Then a heated indoor pool, an outdoor pool, the sea, and fresh water last. The gaps matter as much as the order. A hot tub sits further from a lane pool than a lane pool does from the beach, and an unrinsed beach suit sits further still from a rinsed, shade-dried one. What you do in the twenty minutes after a swim moves the needle more than which water you chose.
The one habit that answers both
- 01Rinse in cool water for a full two minutes, salt or chlorine alike. Cool rather than warm — heat relaxes elastane and helps dye on its way out.
- 02Rinse before the suit dries, not that evening. Chlorine keeps reacting in damp fabric, and salt crystallises the moment water leaves.
- 03Work the water through seams and lining, where salt and grit collect and a surface rinse never reaches.
- 04Press the water out flat, between your palms or in a towel. Never wring — twisting is what sets a crease into elastane permanently.
- 05Dry flat in the shade, never on hot stone, a radiator or a sunny windowsill.
- 06Hand-wash gently with a mild detergent after a chlorinated or sandy swim, and rotate two suits so neither goes back on wet.
Fabric decides where you start. Chlorine and UV resistance in the fibre slows both pathways at once, a dense knit spreads abrasion across more yarn so each filament does less work, and a full second layer means a thinning outer face is not the only thing keeping a suit opaque. Ours is a double-lined sculpting Italian jersey woven at a family mill on Lake Como, chlorine and UV resistant, with shells spun from regenerated ocean nylon. No fabric is immune to either water, but a good one widens the margin considerably. The routine is the same whichever one you swim in: rinse in cool water after every swim, hand-wash gently, never wring, dry flat in the shade.