How to identify real silk: 5 tests before buying on sale

In short — “satin” describes a weave, not a material; the term “100%” is regulated under European law; and five minutes is all it takes to check a fabric without leaving home. Here’s the order I follow and what each test actually proves.

As the big sale weeks approach, the same scene plays out again. A product listing advertises “luxury silk satin,” the photo looks stunning, the price has been cut in half — and the composition is nowhere to be found. It’s not always deception. More often, it’s convenient vagueness. So let’s learn to read before we buy.

“Satin” says nothing about the material

Satin is a weave: a way of interlacing warp and weft threads to create a smooth, reflective surface. Satin can be woven from silk, polyester, viscose or cotton. Saying a pillowcase is “satin” describes its appearance, not its fiber. I’ve explained this confusion in detail in silk or satin: what’s the difference, because it’s behind almost all the misunderstandings.

The same goes for the phrases that crop up during sale season: “silk touch,” “silk effect,” “silky,” “silk-like.” None of them refers to fiber produced by the silkworm. They describe how something feels, and no one is accountable for them.

What the label is required to tell you

There is, however, a solid safeguard. Regulation (EU) No 1007/2011 requires every textile product placed on the European market to state its fiber composition using designated terms. “Silk” is one of them and may refer only to fiber from the silkworm. The same regulation reserves the terms “100%,” “pure” and “all” for products made exclusively from a single fiber.

The practical takeaway is simple: a page that touts “luxury” and “softness” without ever stating a fiber percentage has already told you something. And “100% satin” is not a composition statement — it’s a phrase that doesn’t exist.

Three formulations to know how to distinguish

• “100% silk” — a single fiber, from the silkworm. It’s the clearest wording there is.
• “95% silk, 5% elastane” — a deliberate blend, and a perfectly legitimate one: a few percent elastane gives a garment that needs to follow the body some stretch. L’s essential that it’s stated.
• “Silk satin,” “washed silk,” “charmeuse” — terms describing the weave or finish. They can accompany a composition. They never replace it.

At Studio, the composition is listed on every product page, including when an item isn’t pure silk. It’s less flattering than an adjective, but it’s verifiable—and it’s also, as I wrote recently, what primarily explains the price of silk.

Five tests, from the most harmless to the most definitive

The first four can be done on the item itself without damaging it. The fifth is destructive: save it for last, and use an isolated thread.

1. The reflection, in oblique light

Hold the fabric up to a window and tilt it slowly. Silk has a sheen that changes hue depending on the angle: champagne turns rosy, pearl gray turns golden. This shimmer comes from the fiber’s triangular cross-section, which breaks up the light. Polyester, on the other hand, reflects a more uniform, whiter, slightly metallic shine that shifts very little as you move.

2. The palm, ten seconds

Place your palm flat and count to ten. Silk takes on the warmth of your skin almost immediately, then stays that way. Synthetic satin stays cool a little longer, then suddenly warms up and becomes slightly damp under your palm. This is, in miniature, what you’ll feel all night.

3. Creasing

Grip one corner in your fist for five seconds, then let go. Silk keeps fine, soft creases that disappear on their own after a few hours hanging. Polyester comes out of your fist almost untouched: that’s an advantage in a suitcase, and a clue for you.

4. The water drop

Place a drop on an inconspicuous spot. Silk absorbs it: the area darkens, then dries without a ring. On polyester, the drop beads on the surface and wipes away without leaving a trace. The reason lies in the nature of the fibers themselves — silk is a protein that naturally retains moisture, whereas polyester is a hydrophobic polymer. Textile science cites markedly different ranges: around 11% moisture regain for silk, compared with less than 1% for polyester.

5. The flame, as a last resort

Take a single thread from an inside seam — never from a visible surface. Work over a sink, away from anything flammable, with something to put out the flame within reach. Silk, a protein, burns slowly, smells like burning hair or feathers, and leaves a small black lump that crumbles into powder between your fingers. Polyester melts before it burns, drips, gives off a faint chemical smell and leaves a hard bead that can’t be crushed. A blend does both.

This test causes damage, even to a single thread. Don’t perform it on a borrowed item or on an order you plan to return.

What this difference means once you’re in bed

Moisture regain isn’t just a laboratory nicety: it’s exactly what happens between a cheek and a pillowcase over seven hours. A fiber that absorbs a little perspiration and then releases it leaves skin dry; a hydrophobic fiber keeps it on the surface. That’s what causes the feeling of fabric sticking to you in the early morning, which many people blame on the heating when it comes from the fabric.

Two details are all you need to assess a piece: the composition and the weight. The latter is measured in momme and is worth a closer look — I’ve written a complete guide to it. For bedding, our pillowcases start at 19 momme, the threshold below which a pillowcase wears out quickly in the wash.

The checklist before you click

1. Check the fiber percentage. S’if you can’t find it on the product listing, write to the seller. If they don’t give a clear answer, assume it isn’t silk.
2. Check the momme weight. A reputable product listing will specify it. One that talks about “premium density” without giving a number won’t.
3. Look for words that don’t name a fiber. “Effect,” “feel,” “style,” “like”: these are adjectives, not materials.
4. Compare with market prices. A set advertised as “100% silk, 22 momme” for twenty-nine euros isn’t a bargain; it’s a misrepresentation.
5. Read the care instructions. A recommendation to wash at 60 °C or tumble-dry is a confession: silk can’t withstand either. I’ve detailed the labels and grades that actually mean something.

Frequently asked questions

Is the flame test really reliable?

It’s the most telling of the five, because it distinguishes a protein from a plastic polymer. It has two limitations: it doesn’t quantify a blend, and it causes damage. So it should be done last, on an inner seam thread.

Can silk and satin cost the same?

Rarely. A durable polyester satin can be produced for a fraction of the cost of equivalent silk. When the prices are similar, it usually means one of them isn’t what it claims to be.

What does the term “mulberry silk” tell you compared with “silk”?

It specifies the fiber’s origin: the Bombyx mori silkworm, fed on mulberry leaves, whose filament is long, even, and lustrous - unlike wild silks, which are shorter and more irregular. It’s a useful detail, but it doesn’t replace the percentage.

Is a silk and elastane blend a bad sign?

No, as long as it’s disclosed and justified by the intended use. A few percent elastane in a fitted item is common sense. The problem isn’t the blend; it’s the undisclosed blend.

Can you do these tests on an item received by mail?

The first four, yes, and they won’t compromise your right to return the item. The fifth, no: wait until you’ve decided to keep it.

Shop with confidence

The period ahead is ripe for both great deals and misrepresentation. The simplest filter is still the best: a written composition, a stated momme weight, and consistent care instructions. Our mulberry silk pieces include all three details, and I encourage you to demand the same from any other seller.

— Colette, for the StudioSoie Journal