How to wash swim trunks: one summer, three days it goes wrong

Take one summer with one pair of trunks from Sanwin Beachwear: two weeks by the sea, with a hotel pool for the days it is windy. The calendar below shows what the trunks go through and on which three days things can go wrong. Every heading in this piece belongs to a day in that calendar.

Every day: how do you rinse swim trunks after the sea or the pool?

You rinse them in fresh water, inside and out. That is what we advise in our FAQ: salt from the sea and chlorine from the pool have to come out before they settle into the fabric. The trunks do not have to come off for it, a beach shower or a pool shower is enough. How they dry fast afterwards is in our piece on quick-dry swim trunks.

Day 3: how do you get sand out of swim trunks?

Let them dry first, then shake the sand out: wet sand sticks to mesh, dry sand falls out. What remains you rinse away with the pockets turned inside out and the inner brief from the inside. Where sand hides differs per model. A Tampa has two side pockets, a back pocket with a zip and an inner brief of fine mesh, so start with the three pockets and then rinse the mesh.

Day 6: how do you get a sunscreen stain out of swim trunks?

With dish soap and a handwash in the sink, on the holiday itself. A yellow or orange stain probably comes from avobenzone, a UV filter in many sunscreens, reacting with the iron in hard water. That is what laundry maker Tide and sunscreen maker Sun Bum say in a piece by CBS News from August 2024. Sun Bum calls it rare: it mostly happens with water that is high in iron.

This is how you get it out, with the steps of stain expert Mary Gagliardi in the same CBS News piece. She finishes in the machine; on holiday you do that by hand, at the temperature from the care instructions of the trunks:

1. Massage some dish soap into the stain and leave it for 5 minutes.
2. Rinse it out.
3. Let a stain remover without bleach soak in for 10 minutes.
4. Wash them by hand in the sink, in water of 30 degrees at most with a little detergent for delicates, and rinse until there is no foam left in the fabric.
5. Hang them on a line to dry. If you still see the stain, start again.

Prevention is easier. Put your sunscreen on half an hour to an hour before you go into the sun, and it has soaked into your skin before it touches the fabric.

Day 14: what do you do with wet swim trunks in your suitcase?

At home they are the first thing out of the suitcase, you wash them the same day and hang them outside on the line. A musty smell comes from bacteria and mould in the fabric, and the outdoor washing line is the best remedy for that. "Drying on the washing line outdoors turned out to be the most effective drying method for reducing microorganisms such as bacteria or fungi," says a July 2024 release from Forum Waschen, quoting Professor Dirk Bockmühl of Rhein-Waal University (translated from German). Its members include Stiftung Warentest and the German Environment Agency. According to the Forum, it is mainly the UV in sunlight that works against the germs; a bright or dark pair of trunks goes in half shade, so the colour does not shift.

On the way back they travel in a bag of their own at the top of the suitcase, not between your clothes. At home you find them straight away, and the beach vacation packing list has room for that bag.

At home: can you wash swim trunks in the washing machine?

Yes, at 30 degrees on the handwash cycle, with a detergent for delicates and with similar colours. That is what the care instructions of every pair of Sanwin Beachwear swim shorts say. Afterwards do not wring them and keep them out of the tumble dryer.

October: how do you store swim trunks over winter?

Clean and bone dry. Wash them one last time after the last summer day, let them hang for a day and only then fold them into the closet. On the Tampa we give a 5 year warranty, and a summer without a dryer is what that fabric asks of you. Or you take them out again in December, for a week of winter sun. If you would rather start next year with another print, discover the men's swim shorts or have a look at the Tampa swim shorts.