How to Wash a Gi (Judo / BJJ)
Non-pre-shrunk gis shrink 10–15% in the first hot wash — most practitioners exploit this deliberately to size down. The multi-layer collar shrinks at a different rate from the body fabric: pre-soak before the first wash to equalise moisture and prevent collar warping. Blood from training always needs cold water first. Wash after every session — sweat-saturated canvas is an ideal environment for MRSA.
The Chemistry
A gi (also written as kimono or keikogi) presents a unique combination of heavy cotton construction, heavy-use hygiene requirements, and a very specific shrinkage dynamic that most cotton garments do not share. Gis are made from thick cotton canvas, typically in one of three weave constructions: single weave (lightest, 350–550 gsm), pearl weave (a ribbed textured weave pattern, 400–550 gsm), or double weave (the heaviest, 750–1000 gsm). The specific weave construction affects how the gi shrinks, how it performs in washing, and how long it takes to dry. Double weave gis take significantly longer to dry than single weave — a fully wet double weave gi can weigh 2–3 kg and takes 12–24 hours to air dry completely. Storing a wet or damp gi causes rapid bacterial growth and mould development in the dense weave interior; the gi should never be put away damp. The shrinkage dynamics of gis are deliberately exploited by practitioners. Cotton fibre (cellulose polymer) is spun under mechanical tension; the spinning process extends individual fibre polymers in the machine direction, storing potential energy. Heat and agitation during washing release this tension: fibres contract back toward their equilibrium length, causing shrinkage in both length and width. In most cotton garments this is an undesirable side effect; in gis, it is often used intentionally to size-down the gi. A "pre-shrunk" gi has been processed by the manufacturer through a pre-washing or Sanforization process (mechanical pre-shrinkage using rollers under tension) to remove most of this initial shrinkage — but residual shrinkage of 3–5% typically remains possible even in pre-shrunk gis. A non-pre-shrunk gi will shrink 10–15% or more over its first several washes, with the majority occurring in the first 1–2 hot washes. Many BJJ and judo practitioners deliberately buy a gi one size larger than their usual size and wash it progressively in warmer water to shrink it to a precisely fitted size. Gi collars are the most complex washing consideration. The collar of a gi is constructed from layers of thick cotton canvas stitched together, creating a very dense, rigid structure. In high-quality gis, the collar is reinforced with sashiko-style thick weave cotton layering. This multi-layer collar construction has a higher shrinkage potential than the body fabric — and crucially, it shrinks preferentially in the width direction (causing the collar to become thicker and shorter) when washed at high temperatures. If the body fabric and the collar fabric shrink at different rates, the collar can warp, twist, or pucker. Pre-soaking the gi before the first wash (letting the whole garment wet out gradually) helps equalise the moisture content throughout the construction and allows differential shrinkage to happen more uniformly. Blood stains are very common in gis from training. Blood contains haemoglobin — an iron-containing protein. Heat denatures haemoglobin protein (exactly as it cooks an egg), permanently bonding it to the fabric in a form that detergent cannot dissolve. The correct treatment is always cold water first. Pre-treating with cold water immediately after training, before washing, prevents the protein bonds from forming. Cold water + enzyme (biological) detergent effectively removes blood. Hot water at any stage after the stain has partially dried will fix a permanent brown stain. Gi hygiene is critical for martial arts etiquette and safety. Sweat-saturated gis that are not washed quickly develop bacterial biofilm (Staphylococcus, corynebacteria) and fungal growth. The dense weave provides ideal conditions for microbial growth. Training mats are a major source of MRSA and other bacterial contamination in martial arts facilities — this makes prompt washing at 60°C (for cotton gis) the recommended standard for reducing transmission risk. White vinegar (30 min pre-soak before washing) disrupts bacterial biofilm and significantly reduces bacterial count before the main wash.
Step-by-step
- 1
Rinse blood immediately with cold water before any washing — hot water makes blood stains permanent
If there is blood from training on the gi, rinse with cold water immediately after the session — before the gi is washed or stored. Haemoglobin protein denatures (permanently cross-links) when heated, bonding to fabric in a form that enzyme detergent cannot remove. Cold water rinsing physically removes most fresh blood before denaturation can occur. If blood has partially dried: soak in cold water for 30–60 minutes, then apply enzyme detergent directly to the stain, leave for 15 minutes, then proceed to machine washing. Never use hot water on blood stains.
- 2
Pre-soak in cold water before the first wash of a new gi
For new (especially non-pre-shrunk) gis: soak the entire gi in cold water for 30–60 minutes before the first machine wash. This equalises the moisture content through the gi before it enters the machine, which helps the multi-layer collar construction and the body fabric begin shrinking at a similar rate. Without pre-soaking, the more absorbent inner collar layers and the less absorbent outer canvas can shrink differentially, causing collar warping. White vinegar soak (250ml in a basin of cold water, 30 min) also disrupts any bacteria from pre-delivery handling.
- 3
Determine your washing temperature based on shrinkage goal and weave type
For maintaining current size (pre-shrunk gi): 30–40°C. For controlled shrinkage (non-pre-shrunk gi, sizing down): 60°C for significant shrinkage (2–4 size numbers down), or step up in temperature across successive washes for controlled gradual shrinkage. Single weave gis shrink more quickly and dramatically than double weave. Never wash at 90°C — this can cause significant fibre damage to thick cotton canvas. White gis: 60°C is appropriate for hygiene. Coloured gis: 30–40°C to prevent fading (the dyes in coloured gis have relatively poor wash fastness compared to modern apparel dyes).
- 4
Machine wash on a regular cycle — gis are heavy enough to need thorough washing
A saturated gi is very heavy — load the machine appropriately and wash the gi alone or with one other gi, not with a full mixed load. Use biological (enzyme) detergent for sweat, blood, and mat contamination breakdown. No fabric softener — fabric softener reduces the grip and texture of cotton canvas, which affects performance and mat contact. No bleach unless the gi is white and has heavy contamination (occasional oxygen bleach treatment is acceptable for white gis). Turn coloured gis inside-out to preserve dye.
- 5
Hang to air dry immediately — never store damp; double weave takes 12–24 hours
Remove the gi from the machine immediately and hang to dry. A wet gi left in the machine drum or rolled up in a bag will develop mould and bacterial growth within hours because of its density. Hang vertically from the collar on a thick wooden or padded hanger, or hang from the belt loops of the trousers. Turn inside-out if hanging in a location with some sunlight — UV fades coloured gi dyes rapidly. Double weave gis take 12–24 hours to fully dry in normal indoor conditions. Check the interior of the jacket collar layers by squeezing — if any residual moisture is felt, continue drying.
- 6
Check for collar warping or sizing — reshape while still damp if needed
If the collar has warped or become uneven after the first few washes, reshape it while the gi is still slightly damp: lay the gi flat on a surface and manually press the collar flat and even. The collar cotton will hold the shape it dries in while still damp. Ironing the collar with a cotton setting (200°C) while damp can flatten and reshape a warped collar. For belt: wash the belt separately from the gi — the dense belt absorbs dye from some coloured gis and can transfer colour to the gi body.
Gi weave comparison
| Weave | Weight | Shrinkage risk | Dry time | Wash temp | Notes |
|---|---|---|---|---|---|
| Single weave | 350–550 gsm | High (10–15% non-pre-shrunk) | 4–6 hours | 30–60°C (goal-dependent) | Lightest; most dramatic shrinkage; dries fastest |
| Pearl weave | 400–550 gsm | Moderate–High | 6–10 hours | 30–60°C | Ribbed texture; most popular BJJ weave |
| Double weave | 750–1000 gsm | Moderate (less relative shrinkage) | 12–24 hours | 30–60°C | Heaviest; most durable; very slow to dry — never store damp |
| Gold weave | 500–700 gsm | Moderate | 8–12 hours | 30–60°C | Balance of weight and shrinkage; common in competition gis |
Frequently asked questions
How do you stop a gi from shrinking?
If the gi is pre-shrunk, wash at 30–40°C to minimise further shrinkage — most residual shrinkage potential has been removed during manufacture. For a non-pre-shrunk gi that has already reached your target size: always wash cold (30°C) from that point on. Avoid tumble drying — heat causes ongoing shrinkage even in pre-shrunk gis. Line dry instead. Note that some practitioners intentionally wash at higher temperatures to continue sizing down; once your gi is the right size, switch to cold washing and air drying.
How do you remove blood from a gi?
Act immediately with cold water — never hot. Rinse the bloodstained area under cold water as soon as possible after training. If the blood has dried: soak in cold water for 30–60 minutes to rehydrate the stain, then apply biological (enzyme) detergent directly and leave for 15 minutes before machine washing cold. The protease enzymes in biological detergent break down haemoglobin protein effectively. Never use hot water or put a blood-stained gi in a hot wash — heat denatures the haemoglobin protein, permanently bonding the brown residue to the cotton.
How often should you wash a gi?
After every single training session. Gis become saturated with sweat during training and the dense cotton canvas weave provides ideal conditions for bacterial growth — Staphylococcus aureus, including MRSA strains, thrive in sweat-saturated canvas at body temperature. Training mats are a common source of bacterial transmission in martial arts facilities. Washing at 60°C after each session is the hygiene standard. A gi should never be worn for a second session without washing first — this is a core martial arts etiquette rule as well as a hygiene requirement.
How do you shrink a gi that is too big?
Wash in progressively warmer water across successive washes. Start at 40°C for the first wash after the initial cold pre-soak, then 60°C for subsequent washes until the target size is reached. Most single-weave gis will shrink 10–15% total across the first 3–5 hot washes. Tumble drying also accelerates shrinkage but risks collar warping and is not recommended as the primary shrinkage method. Check the size after each wash while the gi is slightly damp — cotton gi fabric stretches slightly when worn, so the fit when dry is the accurate measure.