What GSM measures, and what it does not
GSM stands for grams per square meter. It tells you how much a piece of fabric weighs for a given area. It is measured on the fabric, not on the garment, and it is tested to methods such as ISO 3801 or ASTM D3776.
GSM is useful because it correlates with opacity, warmth and a sense of substance. It does not measure stretch, softness, durability or wicking on its own. Two fabrics at the same GSM can feel completely different if one is a tight interlock and the other a loose jersey, or if one has 24% spandex and the other 10%. Treat GSM as one line on the fabric sheet, read alongside composition, knit and finish.
Reference weights across a yoga line
| Product or fabric | Reference weight | What drives the choice |
|---|---|---|
| Performance leggings, nylon / spandex interlock | 230-280 GSM | Opacity in deep flexion, hold |
| Gym and fitness leggings, polyester / spandex | 230-280 GSM | Opacity, print base, value |
| Brushed nylon / spandex | 220-280 GSM | Soft hand; brushing adds weight |
| Winter-weight brushed styles | 260-320 GSM | Warmth for cold studios and outdoors |
| White and pastel leggings | Often 280-300 GSM | No dye depth to hide skin |
| Bras, tops, loose and natural-fiber pieces | Confirmed on the fabric sheet | Support, drape and layering |
The table gives starting points. The exact weight for your program is set on the fabric sheet the mill confirms, with a tolerance, before sampling starts.
Leggings: weight and opacity
For leggings, GSM is mostly about opacity. Most premium performance leggings sit between 230 and 280 GSM. Dark colors may pass a deep squat at 230-240 GSM. White and pastel colors often need 280-300 GSM in the same construction, because a light shade has no dye depth to hide the skin beneath a stretched fabric.
This has a planning consequence. If your leggings range runs from black to sand to white, either the lighter colors need a heavier version of the fabric, or the whole range moves up in weight. Decide this before booking fabric, not after a light-color sample fails. Our note on the squat-proof test explains how to run the opacity review, which is a practical sample check rather than an official standard.
Bras: weight is not support
Buyers sometimes assume a heavier fabric gives a more supportive bra. Support mostly comes from the band, the cut, the straps and the cups or lining, with fabric stretch and recovery playing a part. A bra fabric is often chosen to match the leggings in a set, so color and hand line up, and then the construction is adjusted for support. Write the bra fabric weight on the fabric sheet, but judge support on the sample. See sports bra support levels.
Tops and layers: lighter, with care
Tank tops, tees and layering pieces are usually lighter than leggings so they drape and breathe. The risk at low weights is sheerness in light colors and curling at cut edges in single jersey. If a top is meant to be worn alone in a light color, review it on a fit model under studio lighting, just as you would a legging. The exact weight is confirmed on the fabric sheet for the chosen fabric.
Winter weight: warmth without stiffness
Brushed fabrics in the 260-320 GSM range are used for cold studios, outdoor practice and transitional wear. At these weights, spandex share matters even more. A heavy fabric with too little spandex feels stiff, so ask for the composition alongside the weight and test the sample in deep bends. Our spandex percentage note explains the balance.
Tolerance: the number has a range
A nominal GSM is a target, not an exact value. A common tolerance is about plus or minus 5% of the nominal weight. On a 250 GSM fabric that is a band of roughly 238 to 262 GSM. Write the tolerance on the fabric sheet so that inspection has a clear pass and fail, and ask for the test method to be named.
GSM and other numbers on the sheet
Weight interacts with several other properties. Heavier fabrics generally resist bursting better, which you can check with ASTM D3786. Weight does not predict pilling, which depends on yarn and finish and is tested to ASTM D4970 or ISO 12945-2. And weight does not predict dimensional stability, which is tested after laundering to AATCC 135.
Weight can also matter for compliance. The US clothing flammability rule (16 CFR 1610) exempts certain fabrics from testing, including plain-surface fabrics above a stated weight per square yard and fabrics made entirely of certain synthetic fibers. Whether your fabric qualifies depends on its weight, surface and exact composition, so confirm it with your compliance adviser rather than assuming. The compliance page lists the rules buyers usually handle.
How to write weight into your program
- Choose a target weight per product type from the reference table.
- Check the lightest color in the range and adjust weight for opacity if needed.
- Write nominal weight, tolerance and test method on the fabric sheet.
- For brushed fabrics, write base and finished weight separately.
- Keep the approved swatch with its weight tag as the reference for reorders.
A reorder that drifts in weight is one of the quiet causes of complaints, such as a legging that is suddenly less opaque in the second season. Holding the original fabric sheet and swatch makes drift easy to spot at inspection.
It also helps to measure weight on fabric from the actual production lot, not only on the development swatch. Mills can run a quality slightly differently from one dye lot to the next, and a quick weight check on bulk fabric before cutting catches a problem while it is still cheap to fix. Ask the partner factory to record the measured weight of each incoming lot against the tolerance on the sheet.
Next step
Browse the fabric library to see qualities by weight, then send your styles and colors through the quote form. The desk will propose target weights per style and confirm them with the partner mill on the fabric sheet.