A complete guide to choosing, sizing, and caring for a rash guard, including IBJJF rank colour rules for no-gi competition.
A BJJ rash guard is a form-fitting compression top worn during no-gi training and competition to protect the skin, reduce mat friction, and help prevent the transmission of skin infections. Whether you train in a gi, no-gi, or both, a well-chosen rash guard is one of the most practical pieces of kit you will buy. This guide covers everything from materials and fit to IBJJF rank colour requirements, with a sizing comparison table to help you get the right garment first time.
If you are new to no-gi training, also read our guide to gi vs no-gi BJJ for context on how the two formats differ, and see our no-gi shorts guide for the other half of the no-gi kit equation. For an overview of all BJJ equipment, start at the gear hub.
In the context of Thai gyms, where training halls are often open-sided and temperatures sit above 30 degrees Celsius for most of the year, you might wonder why anyone would choose to wear an extra layer. The answer is practical rather than aesthetic.
A rash guard serves four distinct functions during BJJ training.
In Thailand specifically, many gyms make a rash guard compulsory for all no-gi classes regardless of competition plans. Confirm the dress code with the gym before your first session.
The IBJJF (International Brazilian Jiu-Jitsu Federation) introduced mandatory rash guard colours for no-gi competition to make it visually clear at a glance what rank each competitor holds. The rules apply to the dominant colour of the garment, not to trim, panels, or logos.
The table below summarises the current IBJJF requirement. Always verify against the latest official IBJJF ruleset before competing, as the federation updates its technical regulations periodically.
| Belt Rank | Required Rash Guard Colour | Notes |
|---|---|---|
| White belt | White | Black trim and logos permitted |
| Blue belt | Blue | Black trim and logos permitted |
| Purple belt | Purple | Black trim and logos permitted |
| Brown belt | Brown | Black trim and logos permitted |
| Black belt | Black | Red and white trim permitted |
A predominantly black rash guard is accepted at most belt levels when accompanied by the corresponding rank colour in a trim or side panel. If you are competing for the first time and are unsure, a plain rash guard in your exact belt colour is the safest choice.
ADCC events do not mandate rank-specific colours. Check the ruleset for the specific event you are entering.
The fabric composition of a rash guard directly affects how it performs during training. Most BJJ-specific rash guards use one of two base fabric constructions.
The most common construction, typically 85 to 90 percent polyester with 10 to 15 percent elastane (also sold as Lycra or spandex). Polyester provides durability and moisture-wicking performance. Elastane gives the four-way stretch needed to move freely through full grappling ranges of motion. Sublimation printing, the method used for detailed graphics, bonds permanently to polyester fibres, so printed designs do not crack or peel under normal training use.
A nylon-spandex blend (often 80 percent nylon, 20 percent elastane) feels noticeably softer against the skin and has a slight sheen that some practitioners prefer. The trade-off is that nylon is more prone to snagging on velcro, rough patches of mat, and gi material, which shortens the lifespan of the garment. Sublimation printing does not adhere as well to nylon, so nylon rash guards often use screen printing instead, which carries some cracking risk over time.
If you are training in Thailand, prioritise a lightweight polyester-elastane blend with mesh or ventilation panels under the arms. Heavier compression fabrics trap heat and become uncomfortable within the first round in an open-air gym. A fabric weight of around 200 to 220 grams per square metre is a reasonable starting point for tropical conditions.
Rash guard sizing is not standardised across brands. A medium from one manufacturer may fit like a large from another. The only reliable method is to measure your chest circumference and torso length in centimetres and compare those figures against the specific brand's size chart before purchasing.
The table below gives approximate chest measurements for common BJJ rash guard size labels as a starting reference. Treat these as guides only and always check brand-specific measurements.
| Size Label | Chest Circumference (cm) | Typical Torso Length (cm) | Fit Note |
|---|---|---|---|
| XS | 80 to 88 | 60 to 63 | Suited to lean, shorter-torso athletes |
| S | 88 to 96 | 63 to 66 | Most common for lighter weight classes |
| M | 96 to 104 | 66 to 70 | Mid-range; varies most between brands |
| L | 104 to 112 | 70 to 74 | Common for heavier or broader athletes |
| XL | 112 to 120 | 74 to 78 | Size up if torso is long relative to chest |
| XXL | 120 to 130 | 78 to 82 | Check that torso length covers the waistband of shorts or spats |
A correctly fitted rash guard should stay tucked into your shorts or spats throughout an entire round of rolling without riding up. If the hem repeatedly comes free, the garment is either too short in the torso or too loose in the body.
The choice between long and short sleeves comes down to the balance between coverage and thermal comfort.
Long sleeve rash guards protect the forearms and elbows from mat burn and provide greater coverage against skin contact. Many practitioners training in gi classes wear long sleeve rash guards under the jacket for full-body coverage. In competition under IBJJF no-gi rules, long sleeve rash guards are permitted and often preferred as they leave less exposed skin.
Short sleeve rash guards are significantly cooler in warm environments and are a practical first choice for training in Thailand. They cover the torso where mat burn is most common during guard and mount positions, while allowing the forearms to breathe. If you are going to own a single rash guard, a short sleeve option in your belt colour is the most versatile starting point.
Some practitioners use a long sleeve rash guard for no-gi sessions and a short sleeve version under the gi, where the jacket itself covers the forearms. Both configurations are practical and widely used.
Rash guards are a relatively affordable piece of kit, but poor care shortens their lifespan significantly. Follow these steps to get the most out of each garment.
Once your kit is sorted, find out where to put it to use. CNX BJJ covers no-gi sessions, open mat schedules, and training camps across Thailand, from Chiang Mai to Bangkok and Phuket.
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