What Are Rash Guards Made Of?
The short answer
A rash guard is a stretch knit of polyester or nylon blended with spandex, cut close to the body and sewn with flat seams so nothing rubs against the skin. The specification below is the standard build across BJJ, MMA and swim rash guards.
| Component | Standard specification |
|---|---|
| Fabric | Polyester-spandex or nylon-spandex knit |
| Weight | 180-220 GSM |
| Elastane content | Typically 10-20%, giving 4-way stretch |
| Seams | Flatlock stitching, no raised seam ridge |
| Printing | Dye-sublimation on polyester blends; colours bonded into the fibre |
| Fit | Compression fit; long or short sleeve; men's, women's and youth cuts |
Everything else about rash guard construction follows from these choices, and the sections below explain each one.
Polyester vs nylon rash guards
The main fibre is either polyester or nylon, and the choice decides how the garment prints and feels. Both wick sweat well because neither fibre absorbs much water, and both are blended with the same spandex content for stretch.
| Property | Polyester-spandex | Nylon-spandex |
|---|---|---|
| Sublimation printing | Yes; dye bonds into the fibre, unlimited colours | No; sublimation dye does not bond reliably to nylon |
| Hand feel | Smooth, slightly crisper | Softer, often described as silkier |
| Moisture | Absorbs under 1% of its weight; dries fast | Absorbs slightly more than polyester; still quick-drying |
| Abrasion | High resistance; holds colour under mat friction | High resistance; nylon is a notably tough fibre |
| Typical use | Printed team, club and ranked rash guards | Plain or minimal designs where feel is the priority |
In practice, almost all custom rash guards are polyester-spandex, because clubs and brands want printed designs, and sublimation requires polyester. Nylon-spandex is chosen for plain garments where softness matters more than print.
Why the spandex content matters
Spandex, also sold as elastane or Lycra, is what makes a rash guard fit like a second skin and return to shape. Blended at around 10-20%, it gives the knit 4-way stretch: the fabric extends and recovers along both its length and width, so the garment moves through guard work, sprawls and swimming strokes without restricting or bagging.
Too little elastane and the rash guard resists movement and sags after washing; the blend range exists because recovery, not just stretch, is the requirement. The same principle applies across compression garments; ZipaSports specifies 12-20% elastane in its compression and yoga wear, which runs heavier than rash guards at 240-300 GSM.
A compressive fit is also functional in grappling: a loose garment gives an opponent material to grip, while a tight rash guard offers nothing to hold and stays in place under a gi.
Flatlock seams and construction
Rash guards use flatlock seams: the two fabric edges are butted together and stitched flat, rather than overlapped into a raised ridge as on ordinary garments. With no ridge inside the garment, there is nothing to rub against skin that is already under friction from mats or a gi, and the flat seam stretches with the fabric instead of fighting it.
The rest of the construction serves the same purpose. Panels are shaped so seams sit away from high-friction zones, sleeves are commonly raglan-cut so no seam crosses the top of the shoulder, and the body is cut long so the garment stays tucked during scrambles. On sublimated rash guards, rank colours, club logos and sponsor panels are printed into the fabric itself, so there is no appliqué edge to lift and no print layer to crack as the fabric stretches.
Why 180-220 GSM is the standard weight
Rash guard fabric runs 180-220 GSM because that band balances opacity, durability and heat. Below about 180 GSM a stretched knit starts to turn sheer and tears more easily under grip and mat contact; above roughly 220 GSM the garment holds more heat than grappling or surf sessions allow, and begins to overlap legging-weight territory (240-300 GSM), which is engineered for a different job.
Within the band, the same logic applies as elsewhere in sportswear: hot climates and no-gi summer training favour 180-200 GSM, while rash guards worn under a gi year-round or used daily justify 200-220 GSM. GSM measures grams per square metre and is explained fully in our fabrics and GSM reference.
Ordering custom rash guards
ZipaSports manufactures custom rash guards in Sialkot, Pakistan for BJJ, MMA and swim and water sports in polyester-spandex and nylon-spandex at 180-220 GSM with flatlock seams. Designs are fully sublimated: club branding, ranked colour panels, sponsor logos and individual names, matched to Pantone references, in men's, women's and youth cuts with fully custom size charts.
Minimum order is 20-25 pieces per design, lower quantities are possible on request, and there is no MOQ limit for sportswear brands and companies. A free digital design mockup is provided within 24 hours; a physical sample takes 5-7 days, is charged at sample cost, and the cost is credited against your bulk order. Bulk production takes 15-25 business days after design approval, with express courier shipping worldwide in 5-10 days.
Frequently Asked Questions
Are rash guards polyester or nylon?
Both are used. Polyester-spandex is the standard for printed rash guards because sublimation dye only bonds to polyester; nylon-spandex feels softer and suits plain designs. Both are blended with roughly 10-20% spandex at 180-220 GSM.
Do rash guards actually prevent rashes?
They reduce them. A rash guard puts a smooth, tight, flat-seamed layer between skin and the friction source, whether mats, a gi or a surfboard, which cuts the abrasion that causes mat burn and board rash. It also keeps sweat moving off the skin.
What GSM should a BJJ rash guard be?
180-220 GSM. The lighter end suits no-gi training in warm climates; 200-220 GSM suits daily use and wear under a gi, where durability and opacity under stretch matter more than minimum weight.
Why do rash guards use flatlock seams?
Flatlock stitching butts the fabric edges together and sews them flat, leaving no raised ridge inside the garment. Under mat friction a raised seam would chafe; a flat one does not, and it stretches with the fabric.
Can rash guards be printed with custom designs?
Yes. Polyester-spandex rash guards are dye-sublimated, so club logos, ranked colours and names are bonded into the fibre with unlimited colours and cannot crack or peel. ZipaSports includes a free digital mockup of the design within 24 hours.