How to Wash and Dry Swim Trunks Without Fading or Stretching Them

TL;DR: Rinse your swim trunks in cool fresh water immediately after every swim — salt and chlorine cause more damage than washing ever will. When it's time for a proper clean, use cold water, a mild detergent, and skip the fabric softener entirely. Air dry flat or on a line, never in a hot dryer. Follow these steps and your swim trunks will hold their color, shape, and performance for years instead of a single season.

Most swim trunks don't die from overuse. They die from how they're washed — or more accurately, from how they're neglected between washes.

A pair of swim trunks that gets balled up in a wet towel, tossed into a hot washing machine a few days later, and tumble-dried on high is practically guaranteed to fade, stretch, and lose its quick-dry performance within a summer. The same pair, treated with a few minutes of intentional care, will look and feel great for years.

Here's the definitive guide to washing and drying your swim trunks the right way.

The Golden Rule: Rinse After Every Single Swim

This is the single most important habit you can build, and it takes about 30 seconds.

Saltwater and chlorine are far more damaging to swim trunk fabric than a washing machine will ever be. Salt crystals embed themselves in the fibers and slowly break them down, causing stiffness and fading. Chlorine is even more aggressive — it attacks dyes and degrades elastane (the fiber responsible for stretch and shape retention).

What to do: The moment you're done swimming, rinse your trunks thoroughly in cool fresh water. A shower, a garden hose, or a bathroom sink all work perfectly. You don't need soap for this step — you're simply flushing out the salt or chlorine before it has time to set into the fabric.

This applies whether you swam in the ocean, a chlorinated pool, or a lake. Even fresh water can carry minerals and organic matter worth rinsing away.

If you're traveling and wondering how to keep your swimwear in good shape on the road, quick post-swim rinsing is especially critical when you're packing swim trunks for a trip and wearing the same pair multiple days in a row.

Hand Washing vs. Machine Washing: Which Is Better?

Hand washing is always gentler. If you want your swim trunks to last as long as possible, hand washing is the best option. But machine washing is absolutely fine — as long as you do it correctly.

Hand washing (the ideal method)

1. Fill a basin or sink with cool water.
2. Add a small amount of mild liquid detergent (more on that below).
3. Submerge your trunks and gently agitate them with your hands for one to two minutes.
4. Let them soak for 10–15 minutes if they need a deeper clean.
5. Rinse thoroughly in cool water until no soap remains.
6. Gently press out excess water — never wring or twist.

Machine washing (the practical method)

1. Turn your swim trunks inside out to protect the outer fabric and color.
2. Place them in a mesh laundry bag to prevent snagging and reduce friction.
3. Select the delicate or gentle cycle.
4. Use cold water only.
5. Add a small amount of mild detergent.
6. Remove promptly when the cycle finishes.

The mesh bag is worth the effort. Swim trunks can catch on zippers, hooks, and other garments during a wash cycle. The friction accelerates fading and can damage lightweight liners — especially micro-mesh liners designed for breathability and quick drainage.

Cold Water: Non-Negotiable

Warm and hot water are the fastest way to fade colors and break down synthetic fibers.

Most swim trunks are made from nylon, polyester, or a blend of both — fabrics that perform brilliantly in water but react poorly to sustained heat. Hot water relaxes the structure of the yarn, which leads to stretching and loss of shape. It also opens up fiber pores, allowing dyes to leach out more easily.

Always wash in cold water. This is the simplest rule in the entire guide, and it makes the biggest difference after the immediate rinse.

Choose the Right Detergent (and Skip the Fabric Softener)

Not all detergents are created equal when it comes to swimwear.

Use a mild, liquid detergent. Look for something free of bleach, optical brighteners, and harsh surfactants. A gentle detergent marketed for delicates or activewear will do the job without attacking the fabric. You only need a small amount — swim trunks are lightweight, and using too much soap leaves residue in the fibers that can affect quick-dry performance.

Never use fabric softener. This is one of the most common mistakes. Fabric softener works by depositing a thin waxy coating on fibers to make them feel softer. On swim trunks, that coating clogs the fabric's structure, drastically reducing breathability and drying speed. A pair of quick-dry swim trunks that used to dry in minutes can slow down significantly after just a few washes with softener.

It also degrades elastane over time, which means your waistband and any stretch in the fabric will lose their snap faster.

Avoid bleach entirely. Even "color-safe" bleach is unnecessarily harsh for swim trunk fabrics and can cause irreversible fading and fiber damage.

How to Dry Swim Trunks Without Damaging Them

Drying is where most people undo all the care they put into washing.

Air drying (the right way)

Air drying is the safest and most effective method for swim trunks. Here's how to do it properly:

• Lay flat or hang on a line. Either method works. If hanging, drape the trunks evenly over the line rather than clipping the waistband with clothespins, which can stretch it out.
• Dry in the shade. Direct, prolonged sunlight fades colors and degrades synthetic fibers over time. A well-ventilated shaded spot is ideal.
• Gently press out excess water first. Lay the trunks flat on a clean towel, roll the towel up, and press gently to absorb moisture. This speeds up drying without stressing the fabric.

Modern swim trunk fabrics engineered for rapid drying will air dry impressively fast on their own — often within the time it takes to have lunch or grab a coffee. Fabrics like OceanKnit™, for instance, are designed to dry in approximately 7 minutes, so air drying isn't the hours-long ordeal it is with heavier materials.

The dryer (avoid if possible)

If you absolutely must use a dryer, use the lowest heat setting or a no-heat tumble cycle. High dryer heat is the number-one cause of shrunken waistbands, warped liners, and prematurely faded colors in swim trunks.

That said, the best policy is simple: skip the dryer. Quick-dry swim trunks dry fast enough on their own that a dryer adds risk with almost no benefit.

How to Prevent Odor and Mildew

Mildew and that unmistakable musty smell aren't caused by the ocean or the pool. They're caused by leaving damp swim trunks bunched up without airflow.

The rules for preventing odor:

1. Never leave wet trunks in a plastic bag, gym bag, or pile of wet towels. This is the single biggest cause of mildew in swimwear. Even a few hours in a sealed, damp environment can start bacterial growth.
2. Rinse and hang to dry as soon as possible after swimming. If you can't wash them immediately, at least rinse out the salt or chlorine and hang them where air can circulate.
3. On travel days, rinse your trunks in the hotel sink, press out the water, and hang them on the shower rod or balcony railing overnight. They'll be fresh and dry by morning.
4. If mildew smell has already set in, soak the trunks in a mixture of cool water and a quarter-cup of white vinegar for 30 minutes, then wash as normal. Vinegar neutralizes mildew without damaging the fabric.
5. Make sure trunks are fully dry before storing them. Putting even slightly damp swim trunks into a drawer or suitcase creates a perfect environment for mildew and odor.

A Note on Premium and Recycled Fabrics

If you've invested in swim trunks made from premium or recycled materials, proper care matters even more — not because these fabrics are fragile, but because good care preserves the performance characteristics that make them worth owning in the first place.

Fabrics like Blauw's OceanKnit™, made with recycled marine plastic in partnership with the SEAQUAL Initiative, are engineered with fine, tightly woven yarns to deliver that buttery-soft feel and ultra-fast drying speed. Harsh detergents, fabric softener, and high heat don't destroy the fabric overnight — but they gradually degrade the yarn structure and coating that give it those premium properties.

The care routine is exactly the same as outlined above: cold water, mild detergent, no softener, air dry. The materials are salt water and chlorine resistant by construction, so a quick rinse after each swim is usually all that's needed between proper washes.

Quick-Reference Care Checklist

Key Takeaways

• Rinse immediately after every swim — salt and chlorine cause more long-term damage than washing.
• Cold water only, whether hand washing or machine washing. Heat fades colors and stretches elastic fibers.
• Use mild detergent, skip fabric softener. Softener coats fibers and kills quick-dry performance.
• Air dry in the shade. A towel press-and-roll removes excess water, and well-engineered fabrics dry remarkably fast on their own.
• Never store damp trunks sealed up. Airflow is the best defense against mildew and odor.

FAQ

How often should I actually wash my swim trunks with detergent?
A thorough rinse in fresh water after every swim is sufficient for day-to-day care. A full wash with mild detergent every three to five wears — or whenever you notice sunscreen buildup, odor, or visible grime — is usually enough.

Can fabric softener permanently damage swim trunks?
It won't destroy them in one wash, but repeated use coats the fibers with a waxy layer that reduces breathability and slows drying speed over time. It also breaks down elastane, leading to a stretched-out waistband and loss of shape. It's best to skip it entirely.

Is it okay to dry swim trunks in direct sunlight?
Brief sun exposure is fine and can even help eliminate bacteria. But prolonged, repeated exposure to intense direct sunlight accelerates color fading and weakens synthetic fibers. Shade or indirect light is the better default.

My swim trunks already smell musty — can I save them?
Usually, yes. Soak them in cool water with a quarter-cup of white vinegar for 30 minutes, then wash with mild detergent and air dry completely. If the smell persists after two rounds, the mildew may have set in too deeply to fully remove.

Do quick-dry swim trunks need different care than regular swim shorts?
The care routine is the same, but avoiding fabric softener is even more important. Quick-dry fabrics rely on their fiber structure to shed water rapidly, and any coating that clogs those fibers — from softener, heavy detergent residue, or sunscreen buildup — directly reduces their drying speed.