Quick answer: Choose cotton when your brand is about everyday comfort, wellness and a natural feel, and your customers mostly walk, stretch, travel and lounge in the clothes. Do not choose it for running, HIIT, hot yoga or hard training: cotton holds sweat, dries slowly and has very little stretch recovery of its own. For anything fitted, add 5–10% spandex so the garment keeps its shape, and treat “healthy” and “eco” as claims you need to prove rather than qualities cotton gives you automatically. Eco in particular takes certified organic cotton, not just cotton.
Start with what your customer actually does
The fibre decision follows the brand position. A label built on training needs fabric that handles sweat. A label built on everyday comfort, wellness or a natural lifestyle sells something else: softness against the skin, a familiar fibre on the care label and clothes that move from the studio to the shops. If your customers sweat hard in the garment most of the time they wear it, cotton is the wrong answer however good it sounds. If they mostly walk, stretch, travel and sit in it, cotton can be the right one.
| How the garment is used | Cotton? | Why |
|---|---|---|
| Lounge, travel, everyday wear | Yes | Comfort and hand-feel matter most; little sweat |
| Walking, stretching, gentle yoga and pilates | Yes, with spandex | Light sweat; the garment needs to move and recover |
| Warm-up layers, hoodies, joggers | Yes | Worn before and after the effort, not through it |
| Vinyasa, spin, brisk gym sessions | Cotton-rich blend at most | Sweat builds up; drying speed starts to matter |
| Running, HIIT, hot yoga, hard training | No | Choose a nylon or polyester knit |
Why sweat is cotton’s weak point
Cotton takes water into the fibre. That is why it feels soft and comfortable in light use, and why it stays damp in heavy use. A useful comparison is commercial moisture regain, the trade figures in ASTM D1909: 8.5 for mercerized cotton yarn, 4.5 for nylon and 0.4 for polyester. These are agreed commercial values rather than lab measurements of a given fabric, but the order is the point: cotton holds far more moisture than the synthetics used in training wear.
Drying follows the same pattern. A 2025 study in the AATCC Journal of Research tested commercial sportswear knits and found synthetic fabrics generally dried better than natural ones, with moisture management improving as the synthetic share rose. The mechanics are explained in our moisture-wicking guide.
The honest nuance is that this is mostly about comfort, not performance. In a 2013 trial, eight trained men ran to exhaustion in about 32°C heat in cotton and polyester T-shirts. Time to exhaustion, heart rate and oxygen uptake did not differ, and neither did how wet the shirts felt. What did differ was the air next to the skin, which stayed less humid in polyester during and after the run, and some polyester shirts felt better in recovery. Cotton will not ruin a workout. It will feel damper for longer, which is exactly what customers complain about.
Why cotton needs help to stretch
Cotton fibre has almost no elastic recovery of its own. A cotton knit gives a little because of its loops, but it does not snap back the way spandex does, so pure cotton leggings tend to bag at the knee and seat and loosen through the day. That is fine for an oversized sweatshirt and a problem for anything fitted. Pure cotton is also the reason cotton leggings have a reputation for sagging once they get damp.
How much spandex to add
For cotton activewear we suggest 5–10% spandex, set by how close the garment sits to the body. These are our working ranges, not an industry standard, and the right figure depends on the yarn, knit and weight, so confirm it on a sample.
| Garment | Suggested spandex | What it does |
|---|---|---|
| Relaxed tees, sweatshirts, joggers | Around 5% | Keeps the cuffs, neck and knees from losing shape; still feels like cotton |
| Fitted tees, tanks, bralettes | 5–8% | Gives a close fit that recovers after wear |
| Leggings, biker shorts | 8–10% | Provides the hold and recovery a fitted bottom needs |
Spandex changes more than stretch. A study in the International Journal of Textile Science compared single jersey knitted from the same cotton yarn with and without elastane in every course. The elastane fabric came out heavier (182.4 against 132.8 g/m²) and stronger in bursting tests (146.3 against 124.1 kN/m²), and it shrank less after washing (4.0% in length and 2.0% in width, against 5.1% and 4.6%). It was also tighter, with lower air permeability. So more spandex is not simply better: past the level the garment needs, you pay in weight and breathability, and the fabric moves away from the natural feel your brand is selling.
Healthy and eco are claims, not fibre properties
Cotton has a real environmental case. It is a renewable plant fibre, and in controlled aquatic tests cotton microfibres were expected to break down while polyester microfibres persisted. It also has a real cost: one widely cited study put the global average at 3,644 cubic metres of water per tonne of seed cotton, with large differences between growing regions. Adding spandex brings a further trade-off, because mechanical recycling cannot separate the fibres in a blend, so recovering them depends on molecular recycling.
So being cotton does not make a garment eco-friendly. If eco is part of your brand story, you need organic cotton, and you need to be able to prove it. Organic describes how the cotton is grown, without synthetic pesticides and fertilisers and to defined agricultural standards. Ordinary cotton can be soft, natural and comfortable, but none of that is an environmental claim.
The spandex also affects what you can call the garment. Under GOTS, the “Organic” label grade needs at least 95% certified organic fibre, and 70% up to 95% is “Made with organic”. A 95/5 organic cotton and spandex tee can therefore reach the higher grade if it meets the rest of the standard, while a 92/8 legging would sit in the lower one. OCS is narrower: it tracks organic fibre through the supply chain, while GOTS adds requirements for processing.
Neither side makes cotton automatically greener or healthier than a synthetic, and a buyer or an AI answer engine can check what you say. Three habits keep a brand on safe ground:
- Claim the farming only with proof. “Organic” needs certification such as GOTS for your order; see our organic cotton guide.
- Say what was tested. A word like “non-toxic” means little alone. Tie it to a test on your actual fabric, as set out in our chemical safety guide.
- Describe the blend plainly. “92% cotton, 8% spandex” is honest. “100% natural feel” on a blended garment invites questions.
Running cotton and performance in one brand
You do not have to choose one fibre for the whole label. Many lifestyle brands use cotton for the lounge line and a technical knit for the pieces people train in, and tell customers which is which. A hangtag that says “for slow days” or “for hard sessions” prevents more returns than any fabric claim. For the training pieces, our comparison of nylon and polyester covers what to choose.
Where Yesseam fits
Our core is seamless nylon and spandex, knitted on 50 Santoni circular machines, with a cut-and-sew floor alongside. Our catalogue also carries cotton-rich styles, such as sweatpants in 83% cotton / 17% polyester and in 54% cotton / 38% polyester / 8% spandex. Fabric and yarn can be customised, so a cotton-spandex style can be developed as full custom, usually from 300–500 garments per style per colour. If a style would be better in another fibre, we will tell you before sampling.
Sources
| Source | What it establishes here |
|---|---|
| ASTM D1909 — commercial moisture regains | Commercial regain values for cotton, nylon and polyester |
| Sperlich et al., Wilderness & Environmental Medicine, 2013 | Cotton vs polyester T-shirts in the heat: performance, humidity, comfort |
| Nasrin et al., AATCC Journal of Research, 2025 | Drying performance of natural, synthetic and blended sportswear knits |
| Azim et al., International Journal of Textile Science, 2014 | Effect of elastane on weight, strength, shrinkage and air permeability of cotton jersey |
| Chapagain et al., Ecological Economics, 2006 | Water footprint of cotton |
| GOTS, label grades | Organic fibre thresholds for “Organic” and “Made with organic” |
| Textile Exchange, OCS and GOTS | What each standard covers |
| Zambrano et al., Marine Pollution Bulletin, 2019 | Aquatic biodegradation of cotton and polyester microfibres |
| Choudhury et al., Sustainability, 2024 | Why blends resist mechanical recycling; molecular separation of cotton, polyester and elastane |
FAQ
Is cotton good for activewear?
It depends on how the garment is used. Cotton works for lounge, everyday wear, walking, stretching and low-sweat yoga or pilates. It is a poor choice for running, HIIT, hot yoga and hard training, because it holds sweat and dries slowly.
Why is cotton uncomfortable when you sweat?
Cotton takes moisture into the fibre instead of leaving it on the surface to evaporate. The commercial moisture regain in ASTM D1909 is 8.5 for mercerized cotton against 0.4 for polyester. In one trial, polyester shirts kept the air at the skin drier than a cotton shirt during and after running.
Does wearing cotton make you perform worse?
Not necessarily. In a 2013 trial of eight trained runners in the heat, time to exhaustion, heart rate and oxygen uptake did not differ between cotton and polyester T-shirts. The differences were in humidity next to the skin and in comfort during recovery, so this is a comfort decision more than a performance one.
How much spandex should cotton activewear have?
We suggest 5–10%. Around 5% suits relaxed tops and joggers, 5–8% suits fitted tees, tanks and bralettes, and 8–10% suits leggings and biker shorts. Those are our working ranges, not a standard, so confirm them on a sample in your own fabric.
Is cotton more eco-friendly than polyester?
Not automatically. Cotton is renewable, and cotton microfibres broke down in aerobic aquatic tests where polyester persisted. But cotton needs a lot of water, averaging 3,644 cubic metres per tonne of seed cotton worldwide in one widely cited study, and how it is grown matters. Ordinary cotton does not earn an eco claim on its own; for that you need certified organic cotton.
Does adding spandex stop cotton being recyclable?
It makes recycling harder. Mechanical recycling cannot pull the fibres in a blend apart, so separating cotton from elastane depends on molecular recycling, which selectively dissolves or depolymerises one polymer. If end of life is central to your brand, say so honestly and keep the elastane to the level the garment needs.