Swimwear sits at an awkward intersection. It has to stretch, hold its shape, dry quickly, resist chlorine and salt, and survive ultraviolet light — a specification that, for most of the last sixty years, only petroleum-derived elastane and nylon could meet. That is why a garment that weighs less than a hundred grams has a materials footprint out of all proportion to its size.

It is also worn in exactly the environment it pollutes. Synthetic textiles shed microfibres every time they are washed, and a swimsuit is rinsed after almost every wear. Estimates of how much of the microplastic load in the ocean comes from textiles vary widely, but no serious study puts it at zero, and swimwear is the one category worn directly in the water.

The response from the better end of the industry has been twofold: change what the fabric is made from, and change how long the garment lasts. Regenerated nylons such as ECONYL take nylon waste — discarded fishing nets, carpet, industrial scrap — back to virgin-equivalent polymer, which cuts the climate impact of the fibre substantially and, in principle, allows it to be recycled again. That solves the input problem, not the shedding problem.

Longevity is the less glamorous half and probably the more important one. Doubling the service life of a garment from one year to two cuts the emissions associated with producing and disposing of it by roughly a quarter. For swimwear that means construction quality — double lining, bonded seams, properly finished elastic — and it means care: rinsing in cold fresh water, drying flat out of direct sun, and not wringing the fabric. A well-made suit that is looked after will outlast four cheap ones, which is the whole argument in a sentence.