How to Shrink a Rash Guard: What Works (and What Will Ruin It)

Let's be honest from the start: shrinking a polyester-spandex rashguard is almost impossible without destroying its technical properties. Unlike cotton, which shrinks easily with heat, synthetic fibers are designed to maintain their shape. If your rashguard is too big, the real solution is to choose the right size from the beginning.

I'm Félix, founder of Hustle Fightwear and a competitor in BJJ and MMA. I bought rashguards that were too big myself at first, and I tried all the "hacks" you find online. Here's what really works, what doesn't, and what will kill your rashguard.

Why a rashguard doesn't shrink like a cotton t-shirt

A 100% cotton t-shirt shrinks in a hot wash because cotton fibers contract when exposed to heat and mechanical agitation. This is a natural process related to the organic structure of the fiber.

A rashguard is made of polyester (80-90%) + spandex (10-20%). These two synthetic fibers react differently to heat:

• Polyester is thermostable — it does not shrink at domestic washing temperatures. Temperatures would have to exceed 150°C to deform the fiber, which is impossible in a washing machine.
• Spandex is sensitive to heat, but it doesn't shrink — it degrades. Above 40°C, elastic fibers lose their recovery capacity, and compression irreversibly decreases.

Result: heat doesn't shrink your rashguard, it destroys it. You lose compression, elasticity, and sweat-wicking ability — exactly what makes a technical rashguard valuable.

Methods found online (and why they don't work)

High-temperature wash (60-90°C)

This is the most common advice. And it's the worst. A 60°C+ cycle will:

• Destroy the spandex fibers — your rashguard permanently loses its compression
• Potentially fade prints (sublimation) — designs become dull
• Deform the fabric unevenly — the rashguard does not shrink uniformly

Actual result: you don't get a smaller rashguard. You get a damaged rashguard that no longer provides any compression.

Tumble drying

Same problem as hot washing, only worse. Tumble drying combines intense heat + prolonged mechanical agitation. Spandex fibers do not survive multiple tumble dry cycles.

Actual result: the rashguard may deform slightly (not really shrink), but it loses its elasticity and its fit no longer returns to place after stretching. Basically, it becomes loose.

Soaking in boiling water

An extreme variant of hot washing. Same conclusion: you don't shrink polyester, you break spandex. And as a bonus, you risk completely deforming the rashguard's cut irregularly.

The only real solution: choose the right size

If your rashguard is too big, the reality is you need to replace it with the correct size. It's frustrating, but it's the truth: no method can shrink a synthetic rashguard without destroying its properties.

To avoid making the same mistake again:

• Take your measurements (chest circumference + height) before ordering
• Consult the Hustle Fightwear rashguard size guide
• Between two sizes, take the smaller one — a rashguard is meant to be tight
• If you wear it under a gi or for no-gi, an ultra-snug fit is non-negotiable

What to do with your too-big rashguard?

Instead of throwing it away, here are some practical uses:

As a casual base layer. A slightly too-large rashguard is still wearable for physical preparation, weightlifting, or running. The loose fit isn't ideal but it retains its sweat-wicking properties.

As recovery wear. After training, a loose rashguard is comfortable and keeps the torso warm. To understand how long to wear compression clothing for recovery, we have a dedicated guide.

For light training. If you're rolling at low intensity (technical drills, warm-ups), a slightly large rashguard isn't a problem. Reserve your fitted rashguard for sparring and competition.

Frequently Asked Questions

Can a rashguard accidentally shrink?

Not in the strict sense of the word. If you regularly wash it above 40°C or put it in the dryer, it won't shrink — it will degrade. The fabric loses its elasticity, seams can deform, and the overall fit becomes irregular. This isn't shrinking, it's deterioration.

What if my rashguard is just a little bit too big?

If the difference is minimal (between two sizes), you can keep it for training and invest in the correct size for competition. A slightly loose rashguard during training isn't dramatic — in competition, however, the slightest crease is a grip for your opponent.

Do cotton-polyester rashguards shrink?

Blends containing cotton (e.g., 60% cotton / 40% polyester) may shrink slightly in a hot wash. But these blends are not true technical rashguards — they absorb sweat, dry slowly, and do not offer compression. For grappling, stick to 100% synthetic.

Is there a tailoring service for rashguards?

In theory, a tailor can alter a rashguard at the seams. In practice, it's complicated — flatlock seams are specific, and elastic fabric is difficult to work with. The cost of alteration often exceeds that of a new rashguard in the correct size.

Simple rule: choose well from the start

Rather than trying to shrink a rashguard after the fact, invest 2 minutes to take your measurements and choose the right size. Discover the Hustle Fightwear Rashguard collection — precise size chart, flatlock seams, competition-tested anti-friction fabric.