What Is Mulberry Silk? A Plain Guide to the Finest Silk There Is

Mulberry silk is the silk spun by the domesticated silkworm Bombyx mori — a moth larva fed a single food, the leaves of the white mulberry tree. That one unvarying diet is the whole secret: it produces a fibre so uniform, fine and pure in colour that mulberry silk is regarded as the finest silk in the world. It is the silk in a good pillowcase.

That's the short version. The longer one is a small marvel of biology and patience, and it explains why "mulberry" is the word worth looking for.

So what exactly is mulberry silk?

It's a natural protein fibre produced by a caterpillar building itself a home. As the Bombyx mori larva prepares to become a moth, it secretes a liquid from two glands in its head, which hardens on contact with air into a fine filament — and then spends three or four days wrapping itself in that thread to form a cocoon. Remarkably, each cocoon is a single, continuous strand: unravelled carefully, one has been measured at close to a mile long. Because these silkworms are raised in cultivation (a practice called sericulture) and fed only mulberry leaves, the thread they spin is far more even and refined than silk from wild moths. That consistency is the difference you feel.

What are fibroin and sericin?

They are the two proteins that make up the thread, and the distinction matters more than it sounds. Fibroin is the strong, lustrous core — roughly three-quarters of the fibre, and the part that gives silk its softness, sheen and strength. Sericin is the gum, about a fifth, that coats the fibroin and glues the cocoon together. Most of the sericin is washed away in processing, leaving the smooth fibroin that meets your skin. Fibroin is made of amino acids closely related to those in our own skin and hair, which is part of why silk feels so uncannily at home against the body.

What makes mulberry silk different from other types of silk?

Uniformity, mostly. Wild silks — tussar, eri, muga and the rest — come from moths that eat a varied diet of forest leaves, and their threads are coarser, shorter, and naturally tan or brown. Mulberry silk, from a silkworm that eats nothing but mulberry, is long, smooth, strong and a clean near-white that takes colour beautifully. It is the only silk fine enough, and consistent enough, to be woven into the dense, glassy-smooth surface you want against your face and hair every night. When a fabric is worth resting your skin on, it's almost always mulberry.

Is mulberry silk "real" silk — or is some of it just polyester?

Real mulberry silk is unequivocally real silk — but the word "silk" on a label is doing a lot of quiet work, so it pays to read closely. The catch is usually the word "satin": satin is a weave, not a fibre, and a "satin pillowcase" is very often polyester made to look glossy. Polyester can mimic the shine, but never the breathability, the moisture balance or the gentle, protein-fibre feel of the real thing. The label to trust is "100% mulberry silk", ideally backed by an OEKO-TEX certification that the fabric has been tested for harmful substances. If it only says "silk" or "satin", ask what it actually is.

Why is mulberry silk considered the finest — and why does it cost more?

Because it is genuinely laborious to make, and the quality is real rather than marketed. Every metre depends on thousands of cocoons, each one spun over days by a single silkworm, then carefully reeled so the long filament isn't broken. There is no shortcut and very little machinery can replace the care involved. What you're paying for is that uniform, long-staple fibre — the thing that lets mulberry silk be woven densely, feel substantial, and last for years rather than pilling and fraying. It costs more because it is more; the price is the craft.

What does "22 momme" mulberry silk mean?

Momme is the weight measure that tells you how densely the silk is woven — the silk equivalent of thread count. For pillowcases and bedding, 22 momme is the considered sweet spot: heavy enough to feel substantial, glide smoothly and wear well over years, without becoming warm or stiff. It's the weight we use, and it's worth understanding properly — our guide to silk momme and quality goes deeper.

How do you care for mulberry silk so it lasts?

Gently, and less fearfully than you'd think. Mulberry silk is more robust than its reputation suggests — a cool, gentle wash in a fragrance-free detergent, out of direct sun to dry, and it will keep its sheen for years. The full method is in our silk care guide. Looked after, a good mulberry silk pillowcase is the rare luxury that pays you back nightly — kinder to your skin and your hair than anything else you could sleep on.

If you'd like to feel the difference for yourself, our 22-momme mulberry silk pillowcases are 100% mulberry silk and OEKO-TEX certified.

There's something quietly humbling in it — that the most luxurious thing you can lay your head on each night begins with a small caterpillar, a mulberry leaf, and a single unbroken thread nearly a mile long. Five thousand years on, no laboratory has improved on it. That's the measure of mulberry silk: not that it's expensive, but that it has never needed replacing.