Your jumper is not allergic to you. I will get to that. A garment is a fibre, a construction and a finish, and the law obliges a brand to tell you about the first one only, which is a little like being told a meal contains flour.
Everything below is what a fibre tends to do. How the yarn is spun, how the cloth is woven or knitted, and how it is finished can override the fibre, and often does, so read each section as what usually happens rather than what always will.
Nine people in a hundred say they avoid wool because they are allergic to it. In 2017 a review in Acta Dermato-Venereologica went looking for the evidence behind that and came back nearly empty-handed. Five studies had tested for immediate allergic reaction, all with serious methodological problems. Six claimed delayed allergy and not one stated what counted as a positive result. The best-designed trial took sixty-four people who said they could not wear wool, gave them skin-prick tests, and found nothing.
The itch is mechanical, and the whole of it turns on about thirty microns.
Think of one fibre end sticking out of a knitted surface. Press your arm to it and it does one of two things: it bends, or it pushes back. Which one depends on thickness, and here is the part I enjoy more than I should — the force a fibre can exert before it buckles rises with the cube of its diameter. Make it twice as thick and it becomes eight times harder to bend.
Under about twenty microns, it folds and you feel nothing. Past thirty or so it stops folding and starts pressing, with enough force to trip the C-fibre nerve endings in your skin, which are the endings that report pain.
Your jumper is not irritating you. It is very gently stabbing you.
The finest merino, the grades sold as superfine and ultrafine, runs about 11.5 to 18.5 microns. Lambswool, most high-street wool blends, and the scratchy jumper at the back of your wardrobe do not. Which means the micron count decides whether you can wear something against your skin and the price does not, which is worth knowing before you pay for the expensive one.
Wool is keratin, the same protein as hair, held in shape by sulphur bridges between the protein chains.
It also has a glass transition temperature. That is the point where a material stops behaving like a solid and goes rubbery, and water moves it around. At ordinary room humidity wool’s sits near 40°C. Soak the fibre and it falls to roughly zero.
Which means a presser with a steam iron is not flattening anything. She is warming wool past the point where it stops arguing, putting it where she wants it, and letting it dry there. The shoulder of a jacket, the roll of a lapel, the curve built across a chest: all of it is wool being taken briefly out of its solid state and set down again in a better mood.
Then the sulphur bridges re-form in the new arrangement, and over the years some convert into a tougher single-sulphur link that does not come undone. A good wool jacket does not slowly lose its shape. It slowly commits to it.
Polyester has no bridges to break and re-form. Its shape is set by heat in the factory, which is how a pleated polyester skirt keeps its pleats through every wash, and at the temperatures a tailor’s iron can safely reach it barely moves. So a polyester blazer tends to sit flatter across the shoulder however beautifully it was cut. The iron has very little to say to it.
Flax is stiff and highly ordered and has almost no elastic recovery. Bend it and it stays bent. That is the crease across your lap forty minutes after you sat down, and no finish removes it, because removing it would mean removing the linen.
The same stubbornness is why it lasts. Linen has come out of Egyptian burials still recognisably cloth. A linen shirt bought this summer will very likely outlast most of what you own, and look slept in on most days of that long life.
Blend it with a little viscose and the creasing softens. You lose some of the coolness. Which you want depends on who is going to see you that day.
If you remember one thing from this page, make it this one, because viscose is in a great many high-street dresses.
Viscose is markedly weaker wet than dry. So a viscose dress that came back from the wash hanging differently may not have shrunk at all: it may have been pulled out of shape in the spin, at the moment it was weakest.
Modal and lyocell are made from the same wood pulp by different processes, and both hold up much better wet. Lenzing, which makes the lyocell sold as Tencel, puts it at about 80 per cent of its dry strength when wet, the highest of any cellulose fibre. They usually cost more, and they are an easy thing to look for on a product page.
In a 2014 study, twenty-six people spent an hour on exercise bikes, ten in polyester shirts, ten in cotton and six in blends. The shirts were sealed in bags for a day and then assessed. The polyester ones came out noticeably worse: stronger, sourer, mustier. They were also growing a different group of bacteria, micrococci, which turned up almost only on the synthetic shirts.
Why is still being worked out, and the leading explanation is oil. Fresh sweat barely smells; the smell is what bacteria make from what you leave on the cloth, and the main thing you leave is sebum, the oil your skin produces. A 2020 review notes that sebum is hard to wash out of water-repelling fabrics such as polyester, and that washed polyester still smells more than washed cotton or wool.
It is the right fibre for a raincoat and a harder one for a shirt you will wear all day.
The fibres are very fine, which is what you are paying for, and very short, which is the problem. Short ends work loose from the yarn, tangle with their neighbours, and gather into pills.
The two are the same property. Cashmere that feels like cashmere will almost always pill in the end, and a jumper that pills in its first winter has not necessarily failed. Longer fibres and a tighter spin, which cost more, slow it down.
Elastane is a polyurethane fibre, and it is more easily damaged than the cotton or polyester it is spun with. Heat and chlorine both harm it, which is why care labels on stretch clothes warn against hot washes, hot irons and bleach. How long it lasts depends on the fibre, the wash, the dryer and the wear. No one figure holds across garments, so this page will not pretend to give you one.
In practice, a stretch jean and a rigid one can feel much the same in the fitting room and age very differently, and the stretch is usually what goes first. If you buy things to keep, rigid denim has nothing in it to wear out that way.
Recovery is the other half of the story. Stretch is how far cloth extends; recovery is whether it comes back. In laboratory tests on denim, plain cotton came back about 57 per cent of the way after stretching, cotton spun round a polyester filament about 80 per cent, and cotton spun round both elastane and polyester about 90 per cent. How the yarn is built matters as much as what it contains, and the composition label records only the second. A bagged knee by four in the afternoon is cloth that stretched and did not come all the way back.
| fibre | what it does well | where it lets you down |
|---|---|---|
| Wool | falls with weight, keeps much of its warmth when damp, and can be moulded with steam and an iron, which is what tailoring is built on | moths, and it felts if washed hot |
| Linen | carries heat away from the body and holds a lot of moisture before feeling wet | no elastic recovery, so it creases hard and bags at the knee |
| Cotton | holds the shape it was cut in and softens with washing | absorbs water and stays wet; wears thin where it rubs |
| Silk | light and fluid, yet heavy enough to fall in a true bias | sunlight and deodorant both degrade it |
| Viscose | the most fluid of the common fibres, closest to silk | markedly weaker when wet, so it can distort in the wash |
| Modal, Tencel | viscose made properly: the same drape, far more wet strength | costs more |
| Polyester | holds volume, springs back, dries fast, keeps colour | holds body oil and odour more than cotton, even after washing, and absorbs almost no moisture |
| Nylon | smooth, light, generally more abrasion resistant than polyester | degrades in sunlight faster than polyester |
| Cashmere | very fine, very short fibres, extraordinarily soft | pills, then thins |
| Acrylic | light, bulky, cheap, takes dye well | pills easily and absorbs little moisture |
| Elastane | supplies extension, and sometimes recovery | damaged by heat and chlorine, so hot washes shorten its life |
A garment you have stopped wearing has failed, however well it fitted on the first morning. This is the only test that finally counts.
| improves | holds | deteriorates |
|---|---|---|
| Linen, which softens for years | Wool, if kept from moths | Cashmere, which pills then thins |
| Denim, which takes your shape | Silk, kept out of sunlight | Acrylic, which pills early |
| Cotton twill, which softens | Tencel, which washes reliably | Viscose, which can distort in the wash |
| — | Polyester, which keeps its shape | Elastane, faster in hot washes |
How long you keep something is one of the biggest differences you can make. WRAP, the UK waste charity, estimated that wearing clothes for nine months longer would cut their carbon, water and waste footprints by roughly 20 to 30 per cent each. Per wear, a polyester coat worn two hundred times will almost certainly come out ahead of an organic cotton dress worn five.
Which makes the useful questions ones about fit, cut and how the cloth ages, rather than about the word on the swing tag. Two additions worth having. A single-fibre garment is far easier to recycle than a cotton-polyester blend, which today is mostly very hard to separate, so a blend is close to a one-way trip. And viscose and lyocell can start from the same wood pulp, but lyocell is made in a closed loop that recovers almost all of its solvent, while conventional viscose relies on carbon disulphide, which is much harder to contain. That is a real difference hiding behind two words that look the same.
That is as far as this page goes on the subject. The garment you keep longest is the one that fits, and fit is what the rest of this site is for.
The prickle threshold, the cube law and the finding on wool allergy are from Zallmann M. et al., “Debunking the Myth of Wool Allergy: Reviewing the Evidence for Immune and Non-immune Cutaneous Reactions”, Acta Dermato-Venereologica 97 (2017).
Wool’s glass transition temperature and the sulphur-bridge mechanism of permanent set are standard textile science. The figures used here, around 40°C at ordinary moisture and near 0°C saturated, are from the WoolWise wool processing course notes, module 25.
Polyester and odour: Callewaert C. et al., “Microbial Odor Profile of Polyester and Cotton Clothes after a Fitness Session”, Applied and Environmental Microbiology 80 (2014); and Van Herreweghen F. et al., “Biological and Chemical Processes that Lead to Textile Malodour Development”, Microorganisms 8 (2020).
Denim recovery: Babaarslan O. et al., “Denim Fabrics Woven with Dual Core-Spun Yarns”, in Engineered Fabrics, IntechOpen (2018). Lyocell’s wet strength: Rieter and Lenzing, Processing of Viscose Fibers. Keeping clothes longer: WRAP, Valuing Our Clothes (2012).
Everything else is a general tendency of the fibre rather than a measurement of any one garment, and is written as one. A particular garment can behave differently, because yarn, weave or knit, finish and care all change the result.