Every property people care about in clothing — warmth, breathability, drape, durability, how it smells after a day — traces back to fibre structure. The composition label is where that information is.
Wool
The fibre has a natural crimp, which traps air, which is why it insulates.
It absorbs a substantial amount of moisture as vapour without feeling wet, which is why it regulates temperature rather than just retaining heat.
The surface has overlapping scales, which is why it felts when agitated in hot water, and why washing instructions matter.
Fineness is measured in microns, and it determines whether wool feels soft or prickly. The prickle threshold is around thirty microns for most people, which is why merino at eighteen feels entirely different from coarse wool at thirty-five.
It also resists odour, genuinely, which is a property of the fibre chemistry rather than a treatment.
Cotton
Absorbent, comfortable, cheap and enormously versatile.
It holds moisture rather than moving it, which is why cotton is poor for exertion and excellent for a warm still day.
Staple length — the length of individual fibres — determines quality. Longer staples produce smoother, stronger yarn with fewer ends poking out, which is what long-staple designations refer to.
Loses strength when wet, which is why cotton wears at stress points.
Linen
From flax, with a fibre structure that is stiffer and more conductive of heat than cotton, which is why it feels cool.
Stronger when wet, unlike cotton, which is why linen textiles survive for centuries.
Creases readily because the fibres are stiff and do not spring back, and no finishing entirely removes this. Anyone who cannot tolerate creasing should not buy linen.
Silk
A continuous protein filament rather than a staple fibre, which is why it is smooth and lustrous.
Strong for its weight, poor in sunlight, damaged by perspiration over time.
The weight designation refers to density and determines drape and durability — lightweight silk is delicate in a way heavier silk is not.
Polyester
Strong, holds shape, dries fast, resists creasing, cheap, and dominates global production by a large margin.
Hydrophobic, which means it does not absorb moisture — good for moving sweat away, bad for feeling comfortable in still heat.
Retains odour, because the compounds bind to the fibre surface and washing does not fully remove them. This is a genuine and well documented property.
Sheds microfibres in washing, which is the environmental issue that has received most attention.
Nylon
Stronger and more abrasion resistant than polyester, with better elasticity.
Which is why it appears in hosiery, outerwear shells and anywhere abrasion matters.
Absorbs slightly more moisture than polyester, and degrades faster in sunlight.
Viscose and its relatives
Made from cellulose — usually wood pulp — dissolved and reformed into fibre.
Which makes it neither natural nor synthetic in the usual sense, and its properties are closer to cotton with better drape.
Weak when wet, which is why viscose garments distort in washing.
Production methods vary enormously in environmental impact, from heavily polluting conventional processes to closed-loop systems that recover the solvent. The fibre name on the label frequently does not distinguish them, though some branded versions do.
Elastane
Added in small percentages for stretch and recovery.
It degrades faster than the fibres around it, particularly with heat, which is why stretch garments lose shape before they wear out.
Washing cool and never tumble drying extends this considerably.
It also makes recycling substantially harder, since blended fibres cannot be separated by current mechanical methods.
Reading a blend
Blends combine properties and they are not additive.
A small percentage of synthetic in a natural fibre can improve durability and shape retention meaningfully.
A high percentage generally means the synthetic properties dominate — including odour retention and the feel against skin.
Which is why a wool blend at seventy percent wool behaves like wool, and one at thirty percent does not, despite both being described the same way in marketing.
The label gives the percentages. It is worth two seconds of reading.
Yarn and weave change everything again
The fibre sets the limits, and how it is spun and woven determines what is actually achieved within them.
Worsted wool uses combed, aligned long fibres spun tightly, producing smooth fabric with a clear surface — suiting cloth.
Woollen wool uses shorter fibres spun loosely with air trapped between, producing fuzzy insulating fabric — tweed and flannel.
Same fibre, entirely different fabrics, and the distinction explains why one wool garment is crisp and another is soft.
Weave structures
Plain weave alternates over and under, producing a stable balanced fabric.
Twill offsets the interlacing to create diagonal lines, which produces a more flexible fabric with better drape and hides soiling well.
Satin weave floats threads over several others, producing a smooth lustrous surface that snags easily.
Knits loop rather than interlace, which is why they stretch, and why a run in a knit propagates while a woven simply frays.
Thread count and fabric weight together tell you more about a fabric than the fibre content alone does.