Fibre content on a care label is the most useful piece of information a garment gives you. It tells you how the fabric will behave against sweat, heat and repeated washing long before you feel it against your skin. Below is what each common fibre actually does, and how structure and finish change the result.
Why fibre content is the place to start#
A garment’s fibre list is not a marketing claim. It is a legal disclosure in most markets, and it is usually accurate. Percentages are listed from highest to lowest, so a breakdown tells you the basic physics of the fabric: which fibres absorb water, which repel it, which stretch, which hold odour, and which are sensitive to heat or chlorine.
Two garments that look identical on a rail can behave differently because one is mostly polyester and one is mostly cotton. Knowing which is which saves you from a purchase that feels fine on a shop floor and wrong after the first hard session.
Polyester: the workhorse of technical clothing#
Polyester is hydrophobic, meaning it takes on very little water. That is why it dries quickly and stays light when you sweat heavily. On its own it does not pull moisture away from skin; that comes from the knit structure and from a wicking finish applied to the fibre. Polyester is also oleophilic, a polite way of saying it attracts oils, including the oils in sweat and skincare, which is what keeps a smell in a shirt after several washes. Wash polyester kit promptly rather than leaving it in a bag.
Polyester is strong, resists stretching out of shape and holds up to abrasion well.
Nylon: tougher, with a different relationship to water#
Nylon, also called polyamide, is generally stronger and more abrasion-resistant than polyester and feels a little smoother and cooler. It takes on a little more water and dries a little slower, but it is still hydrophobic in practice. Nylon is common in tights, swimwear and outer layers, where strength and a soft hand matter.
It is sensitive to heat and can stiffen or discolour if dried hot, and like polyester it holds onto oils.
Elastane: the small percentage that changes everything#
Elastane, also sold as spandex or under trade names, is what allows a knit to stretch and recover. It usually appears at a small percentage, and that percentage is worth reading. More elastane means more stretch and more compression, but also more sensitivity: it is damaged by high heat, by chlorine, and by oils including sunscreen and some skincare products. That is why a garment with a high elastane content is the one that goes baggy at the knees and seat first.
The stretch comes from elastane; the durability comes from everything else in the blend.
Merino wool: warmth, odour control and moisture vapour#
Merino is a fine wool that absorbs moisture vapour rather than liquid water, so it can hold sweat in a way that still feels dry against the skin. It resists odour well, because wool fibres naturally limit the bacteria that produce it, and it manages temperature across a wider range than most synthetics.
The trade-offs are real: it is slower to dry than polyester, less abrasion-resistant, needs more careful washing, and costs more because the fibre is harder to produce. For cold-weather base layers and socks that trade is often worth making; for high-sweat gym sessions many people prefer synthetics.
Cellulosic fibres: modal, lyocell and bamboo viscose#
These fibres come from wood or plant pulp and behave more like cotton than like polyester. They absorb water readily, feel soft and cool, and drape well. Lyocell and modal are generally the more robust members of the family; bamboo viscose is soft but can be delicate when wet and may pill with friction.
They appear frequently in yoga wear, casual activewear and blends, where the softness is the point, and are usually paired with polyester or nylon for heavy sweating. Wash them cooler and dry them gently, since heat and agitation cause pilling and shrinkage.
What blend percentages tell you#
A blend is a set of trade-offs, and the percentages point to which way it leans. A fabric that is mostly polyester with a small amount of elastane is built for movement and quick drying. A fabric that is roughly half cotton and half polyester feels softer and absorbs more, and also stays damp longer. A wool blend with a synthetic core gets some of the warmth and odour resistance of wool, with more durability and a lower cost.
Read the list twice: once for the dominant fibre, which sets the overall character, and once for the minor fibres, which usually govern stretch, softness and how the garment will age.
Knits: how the loops change the feel#
Most activewear is a knit, and the structure can matter as much as the fibre. A single jersey is thin, stretchy and tends to curl at the edges. An interlock has two faces and is more stable, which is why it is common in leggings and tops that need to hold shape. Rib knits stretch much more in one direction and are used for cuffs, necklines and some waistbands. Mesh is an open structure built for airflow.
French terry has a smooth face and a looped back, which absorbs some sweat and feels soft and slightly heavier. Brushed fleece has a raised back and traps air for warmth.
Weaves: when a fabric needs to resist rather than stretch#
Woven fabrics are made from interlaced yarns rather than loops. They stretch less, hold their shape firmly and resist abrasion well, which makes them useful for outer layers, training shorts and anything that will be sat on or dragged. A plain weave is the simplest and most stable; a twill has a diagonal surface and usually more durability; ripstop adds a grid of thicker yarns to limit tearing. Stretch wovens combine that structure with elastane, which gives you toughness and enough give to move.
Finishes layered on top of the fibre#
A finish is a treatment applied to the fabric after it is made, and it can change behaviour significantly. Wicking finishes help a hydrophobic fibre move moisture along its surface. Durable water repellent finishes make a fabric shed light rain and are common on outer layers; they wear off with abrasion and repeated washing, and residues from detergent and softener reduce their effect.
Finishes are the least durable part of a garment. When a wicking top stops feeling dry, the fibre has not changed. The finish has.
Reading the label in practice#
Take a photo of the fibre list and care symbols before you commit to a purchase, because tags wear and fade. Compare the fibre content with the job you are asking the garment to do, and treat the care instructions as part of the price. Pick garments whose fibre content and structure match your most common sessions, and accept that no single fabric does everything well: the blend that suits a cold morning run will not be the one that suits a hot studio class.