Every garment has a small label listing its fibre composition as percentages. Most people never read it. It is, in practice, more informative than anything on the product page — it tells you how the garment will feel against skin, how warm it will be, how it will behave when wet, and roughly how long it will last.
Here is what each of the common fibres actually does.
The stretch fibre: elastane
Also sold as Lycra or Spandex — same fibre, different brand names. It appears in almost all support wear at somewhere between 5% and 25%.
Elastane can stretch to several times its length and return. It is what makes a garment hold its shape rather than bagging out. Nothing else in a fabric blend does this job.
What the percentage tells you: roughly 5–10% gives comfortable everyday stretch. 15–20% gives firmer, more noticeable support. Above 20% you are into strong shapewear territory.
Its weakness: heat and chlorine. Elastane is the reason support garments must not go in a tumble dryer or a hot wash — heat permanently relaxes the fibre and the garment stops springing back. It is also the fibre that determines the garment's lifespan; everything else in the blend will outlast it.
The structure fibres: nylon and polyester
One of these two usually makes up the bulk of a compression garment.
Nylon (polyamide) is softer against skin, has a smoother finish, and is the more expensive of the two. It handles repeated stretching well. It absorbs slightly more moisture than polyester, which means it takes a little longer to dry but feels less clammy. Nylon-dominant blends generally feel better next to skin.
Polyester is cheaper, dries faster, holds colour better over time and resists pilling well. It is slightly less soft. It also holds odour more stubbornly than nylon, because odour compounds bind to it — which is why polyester activewear develops a persistent smell that survives washing.
Neither is wrong. If softness matters most, look for nylon. If you want fast drying and colour that stays true, polyester.
The comfort fibres
Cotton is breathable, soft, and the fibre most skin tolerates best. Its weakness is that it absorbs moisture and then holds it — wet cotton stays wet and feels cold. It also has no recovery: cotton stretches and stays stretched. This is why you rarely see high-cotton compression wear, and why a cotton-heavy waistband goes baggy.
Where cotton earns its place is in the parts of a garment that touch skin directly: linings, gussets, the inner layer of a wrap.
Modal is a fibre made from beech wood pulp. It is softer than cotton, drapes better, resists shrinking, and stays soft after many washes rather than going stiff. It is a genuine upgrade over cotton for anything worn against skin, and it costs more.
Viscose and rayon are also wood-pulp fibres, and are very soft and cool to the touch. Their weakness is that they lose significant strength when wet and can shrink. Handle wet viscose gently.
Bamboo is worth a note. Almost all "bamboo" fabric is bamboo viscose — bamboo cellulose processed chemically into a viscose fibre. It is genuinely soft and comfortable. But the marketing claims often attached to it, particularly around antibacterial properties, are frequently not supported once the material has been through that processing. Advertising standards bodies in several countries have taken action over exactly these claims. Buy bamboo viscose because it is soft and pleasant, which it is — not because of a health claim on the packaging.
Merino wool appears occasionally in maternity base layers. It regulates temperature genuinely well, resists odour better than any synthetic, and modern merino is fine enough not to itch. It is expensive and needs careful washing.
Blends you will actually see
- Nylon 80% / Elastane 20% — standard firm compression. Smooth, strong, holds shape. The classic shapewear blend.
- Polyester 85–90% / Elastane 10–15% — the more affordable equivalent. Slightly less soft, dries faster.
- Cotton 90–95% / Elastane 5–10% — soft everyday wear with light stretch. Comfortable, but will not provide firm support and will loosen through the day.
- Modal 90–95% / Elastane 5–10% — premium soft-touch. Common in good nursing bras and sleepwear.
- Nylon / Cotton / Elastane three-way blends — typically a supportive outer with a cotton-rich inner. Often the best of both.
Two things the label will not tell you
Fabric weight. Measured in GSM (grams per square metre), this determines how substantial a fabric feels. Two garments with identical composition can feel completely different at 150 GSM versus 280 GSM. Sellers rarely publish it; if a listing does, that is usually a good sign.
Construction. Flatlock seams lie flat against skin and do not create a ridge. Overlock seams create a small raised edge that can press in over a long day. Bonded or seamless construction has no seam at all. For anything worn under fitted clothing for hours, this matters more than the fibre percentages.
A quick way to use this
Next time you are choosing between two similar items, look at the composition label first. Nylon-based with 15–20% elastane means firm support with a smooth finish. Cotton or modal-based with 5% elastane means soft and comfortable but not supportive. Neither is better — but knowing which one you are buying prevents the most common disappointment, which is ordering something soft when you wanted support, or something firm when you wanted comfort.