Fabric guide

A drop of water marks silk. A full wash does not.

That is not a contradiction, and the reason behind it is the key to the whole fibre. Silk and wool are both protein, but they fail in opposite ways — and almost all the advice you have read about silk is borrowed from wool, where it does not apply.

Last updated 26 July 2026

Silk cannot felt

A wool fibre is covered in overlapping scales that interlock like a ratchet under agitation. That is what felting is, and it is why knitwear must be handled so carefully.

Silk has no scales. The filament is a coagulated stream of fibroin with a surface roughness under ten nanometres — effectively frictionless, with none of wool's cuticle and none of cotton's twist. It is why silk shines, and it is why there is nothing on the surface for another fibre to catch on.

So the single most feared laundry outcome simply cannot happen to silk. Agitation is not what you are protecting it from.

What silk is vulnerable to is chemistry — and light, and, more than anything else in your wardrobe, your own armpits.

It is attacked from both ends of the pH scale

Silk fibroin is amphoteric: it can behave as an acid or a base depending on what surrounds it. That sounds like flexibility and is the opposite.

Alkali swells the filament, prising the silk polymers apart and hydrolysing the forces holding them together. Prolonged exposure goes further and hydrolyses the peptide bonds themselves, which destroys the polymer outright.

Acid is the surprise. Silk is degraded more readily by acid than wool is — so where wool's rule is simply "avoid alkali," silk is squeezed from both directions and needs a genuinely narrow band.

The practical consequence is short: ordinary laundry detergent is alkaline. Use a pH-neutral silk or wool wash. And since silk is a protein like wool, the protease problem applies here too — biological detergent digests fibroin exactly as it digests keratin.

Water rings, and why immersion is safer than a splash

This is the counterintuitive part, and it is ordinary physics rather than anything mystical about silk.

A drop lands and spreads through the fibres. As it evaporates it does so fastest at the pinned outer edge, and that drives a flow of liquid outward from the middle. Anything dissolved in the water — minerals from the tap, whatever the rain picked up — is carried to that edge and deposited there as the drop dries. The ring is a tidemark of everything the water was carrying.

There is a second effect on top. Fibres at the edge swell, shift and dry in slightly different alignment, and on a surface that smooth even a tiny misalignment changes how light reflects off it. The ring can show up even when the water was almost pure. The same physics forms a tideline around any spot treatment, on any fabric.

Sunlight does more damage than washing

The rule almost nobody knows, and the one most likely to be quietly ruining things.

Silk absorbs more ultraviolet light than cotton or wool, and it is nonetheless far more vulnerable to it — UV exposure both fades the dye and breaks down the fibre itself, costing real strength. Museum conservators treat silk as one of the most light-sensitive materials they handle, on the basis that light exposure causes irreversible damage that accumulates and never reverses.

So: never dry silk in sunlight, and do not store it anywhere bright. Hanging a silk shirt on a sunny balcony does more harm than the wash it just came out of.

This is also why so many antique silk garments are shattered along their fold lines. Historic "weighted" silks, loaded with metal salts to add drape and heft, photodegrade faster still.

Your antiperspirant is destroying it

If a silk garment has failed under the arm, this is almost certainly why, and almost nobody attributes it correctly.

Aluminium-based antiperspirants are acidic, and silk is acid-sensitive — that alone would be enough. But aluminium also acts as a catalyst, driving a bonding reaction between itself and the proteins in sweat that produces a yellow, polymer-like residue embedded deep in the fibre.

The cruel detail is the delay. The yellowing develops over time, partly through oxidation of unsaturated fatty acids held as insoluble aluminium salts — so the stain appears weeks after the wear that caused it, long after anyone would connect the two. At the serious end, aluminium chloride can weaken the fabric until the silk simply tears under the arm. People blame the seam, or the shop.

Perfume makes it worse: both the alcohol and the fragrance oils increase how often discolouration shows up.

• Let antiperspirant dry completely before the garment touches your skin.
• Wash silk soon after wearing it. The reaction continues in the wardrobe — storing it soiled is what does the damage.
• Never iron an underarm you have not cleaned. Heat sets the stain permanently.

How to wash it

The silk-specific rules, on top of the general hand-washing method.

• Immerse the whole garment. No spot-cleaning, no dabbing.
• Cool water, and briefly. Long soaks move dye and extend the pH exposure.
• pH-neutral, non-biological. A silk or wool wash. No alkaline powder, no enzymes, no bleach of any kind.
• Do not wring. Not because it will felt — it cannot — but because wet fibroin creases and those creases set.
• Roll in a towel, then dry flat, out of the light.
• Iron damp, on the reverse, on the lowest setting — one dot. Silk scorches easily and shows every mark.

Notice how much of that differs from the wool routine. You can be more robust with the handling here, because there is no ratchet to worry about. It is the chemistry that has to be gentle, not the hands.

The short version

• Silk cannot felt. No scales, nothing to interlock.
• It is damaged by both acid and alkali, and ordinary detergent is alkaline.
• Water rings form at the edge of a wet patch. Wet all of it, or none of it.
• Sunlight is worse than washing. Never dry or store silk in the light.
• Aluminium antiperspirant yellows it and eventually tears it. Let it dry; wash promptly.
• Handle firmly, treat chemically gently. The opposite of wool.

Most of what circulates about silk is wool advice wearing a different label — be gentle, do not agitate, barely let it touch water. It is not wrong so much as aimed at the wrong failure. A silk shirt will survive a confident hand wash for years. What it will not survive is a sunny windowsill, an alkaline detergent, or a decade of antiperspirant. Its label very often says dry clean only, and for an unstructured silk garment that is usually a preference rather than a verdict.