What to wear under a BJJ kimono?

"What should I wear under my BJJ kimono?" This is one of the most common questions among beginners, and even some experienced practitioners still hesitate. The answer depends on several factors: your gender, your comfort level, the temperature of the dojo, and especially the rules of your federation if you compete. At Hustle Fightwear, we explain everything so you arrive on the mat with the right gear, at the right time.

Why wear something under your kimono?

The BJJ kimono (or gi) is designed to withstand pulling and gripping. But it's a thick fabric, abrasive on bare skin, especially after a few washes. Wearing an intermediate layer prevents irritation, sores, and mat burns on the back and armpits.

Second reason: hygiene. Technical undergarments absorb sweat and keep it away from the kimono, which can then air out between washes. It's also an additional barrier against bacteria and fungi (ringworm, staph), unfortunately common on poorly disinfected mats.

Finally, compression: a rashguard or compression shirt supports muscles during effort, which improves comfort and recovery.

For men: rashguard or compression shirt

For men practicing BJJ in a gi, two options are available to you. The short-sleeve rashguard (or sleeveless) is the most classic solution: it protects your torso, absorbs sweat, and easily fits under a kimono. It's also a piece you can reuse if you switch to no-gi. If you're unsure about the size, we've prepared a guide: what size to choose for a rashguard.

A classic compression shirt also works, but it is often less technical (less absorbent, more noticeable seams). This is a viable option if you're a beginner and haven't yet invested in a dedicated rashguard.

Beware of IBJJF rules: in adult male gi competition, IBJJF rules state that you must wear a rashguard or nothing under the kimono. A simple casual t-shirt is not allowed. Always check your competition's rules before showing up.

For women: rashguard + sports bra mandatory

For women, the IBJJF rules are clear: you must wear a short or long-sleeve rashguard under the kimono. This rule applies to both training and competition, and in the majority of serious dojos.

Under the rashguard, a technical sports bra is highly recommended for support. Choose a model without metal underwires (they can cause injury in case of impact), with medium or high impact support depending on your body type.

The winning combination: wireless sports bra + short or long-sleeve rashguard + kimono. You are then supported, protected, and in compliance with federation rules.

The bottom of the kimono: compression shorts or nothing?

The kimono pants (or pants) are thick and loose. To avoid chafing and "flashing" during guard passes, many practitioners wear compression shorts (also called spats or fight compression shorts) underneath.

For men, wearing briefs or boxers under the pants is sufficient if you don't want to invest. Compression shorts remain more comfortable, especially for long sessions. For women, compression shorts are not mandatory but highly recommended for comfort.

Caution in competition: the IBJJF only allows spats under the kimono (not visible), and only certain colors are accepted. Check before weigh-ins to avoid an unpleasant surprise.

Mistakes to avoid

First mistake: wearing a cotton t-shirt under the kimono. Cotton absorbs sweat but retains it, creating a humid environment and promoting irritation and infections. Always opt for a technical fabric (polyester + elastane).

Second mistake: wearing clothing that is too loose under the kimono. The fabric will bunch up, get caught during rolls, and become very uncomfortable. Always prefer a fitted, or even compressive, piece.

Third mistake: ignoring your federation's rules. Some competitors have been refused weigh-ins due to non-compliant undergarments. This is frustrating when you've been preparing for your competition for months.

At Hustle Fightwear, every rashguard and compression shirt is designed to be compatible with wearing a kimono: close-fitting cut, technical materials, flat seams. Enough to get through your next session without irritation or unpleasant surprises on the mat.