Natural or synthetic: when each one is actually better

"Natural fibres good, synthetics bad" is a comfortable rule and a wrong one. It also leads to genuinely worse buying decisions — a cotton raincoat, a wool running shirt, a linen winter coat.

The useful framing is not which family is superior. It is which properties a particular garment needs, and which fibre delivers them.

What each family is actually good at

Cotton

Comfortable against skin, breathable, absorbs moisture readily, takes dye well, cheap at low quality and excellent at high quality.

Its defining weakness is that it absorbs water and holds it. Wet cotton stays wet, loses its insulating value entirely, and gets heavy. This is why cotton is excellent for a t-shirt and dangerous for a hiking base layer.

Wool

Insulates when wet, resists odour to a degree that seems implausible until you try it, regulates temperature across a wide range, and is naturally flame-resistant.

Weaknesses: expensive, felts if agitated, can be damaged by moths, and takes a long time to dry. Merino solves the itchiness that people associate with wool — the fibres are finer, so they bend against the skin rather than poking it.

Wool is the fibre most often underrated by people who have only owned bad wool.

Linen

Strongest of the natural fibres, and the best at moving heat away from the body. Genuinely unmatched for hot weather.

It wrinkles immediately and permanently. This is not a defect to be solved; it is what linen does, and a linen garment sold as wrinkle-free is a blend.

Polyester

Strong, cheap, dries very fast, holds colour, resists wrinkling, keeps its shape.

Weaknesses: does not breathe well, holds body odour stubbornly (bacteria adhere to it more readily than to natural fibres), melts rather than chars, and sheds microplastics in the wash. It also pills where it rubs, and the pills are difficult to remove because the fibres are strong.

Nylon

Stronger and more abrasion-resistant than polyester, with better stretch recovery. Used where things get worn through — sock heels, backpack straps, the elbows of technical jackets.

Elastane (Lycra, Spandex)

Never used alone. Added at 1–5% for stretch and recovery. It is what makes fitted clothes comfortable, and it is genuinely a modern improvement with no natural equivalent.

Its weakness is lifespan: elastane degrades faster than the fibres around it, especially with heat. A garment with elastane has a shorter life than the same garment without, and hot washing shortens it further.

Viscose, rayon, modal, Tencel

Chemically processed cellulose — natural raw material, industrial process. They drape beautifully, feel cool and smooth, and take dye brilliantly.

They are substantially weaker when wet than when dry, which is why viscose garments are so often "dry clean" or "hand wash". Tencel (lyocell) is the strongest of them and made with a closed-loop solvent process, which makes it the most defensible environmentally.

Which to choose, by job

• Next to skin, everyday — cotton or merino. Comfort and odour resistance.
• Base layer for exercise — merino or polyester, not cotton. Cotton holds sweat against you.
• Insulation when it might get wet — wool, or synthetic fill. Down is the best insulator by weight and useless wet.
• Hot and humid — linen, or a linen-cotton blend.
• Outer shell, rain — synthetic. There is no natural alternative that works.
• Something that must hold its shape all day — a blend with a few per cent elastane, or a stable woven.
• Socks — wool with nylon at the wear points, or the heels go through.

The environmental picture is not one-sided either

Synthetics shed microplastics, are made from petroleum, and do not biodegrade.

Cotton is one of the most water-intensive and pesticide-intensive crops grown. Conventional cotton is not a low-impact material. Wool has a significant land and methane footprint.

The largest single factor, on almost every analysis, is neither the fibre nor the manufacturing — it is how many times the garment is worn before it is discarded. A polyester coat worn for ten years is a better environmental outcome than four cotton ones worn for two. Which brings the question back to durability and fit, and to cost per wear.

The short version

• Neither family is better. Each is better at particular jobs.
• Cotton fails wet; wool insulates wet; linen wrinkles by nature; polyester holds smell; elastane wears out first.
• The right question is what the garment has to do, not what the fibre is called.
• The biggest environmental variable is how long you keep it, not what it is made of.