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

Mulberry silk is the silk made by the Bombyx mori silkworm, a small domesticated moth larva raised on a diet of nothing but white mulberry leaves. That single, careful diet is the whole secret. It produces a thread so fine, so pale and so even that mulberry silk is widely held to be the finest silk in the world — the soft, light-catching cloth most people are picturing when they hear the word at all. It also makes up the great majority of the silk produced today.

That's the short answer. The longer one is more interesting, and worth knowing before you spend money on anything called “silk”.

So what exactly is mulberry silk?

Mulberry silk is one continuous protein filament, spun by a caterpillar to build the cocoon it transforms inside. A single cocoon can hold a thread close to a kilometre long, unbroken. That thread is made of two proteins: fibroin, the strong structural core, and sericin, the natural gum that coats and binds it. Unwind several cocoons together, twist them gently, and you have raw silk.

What makes the mulberry kind special is the control. The Bombyx mori has been domesticated for some five thousand years — it no longer flies, and it eats only mulberry. That unvarying diet gives its thread almost none of the knots, colour or coarseness of silk spun by wild moths. The result is long, smooth and naturally near-white, which is exactly why it has been prized since it was first unspooled in ancient China.

Why is mulberry silk considered the best?

Because the fibre itself is longer, finer, smoother and more uniform than any wild silk — and those four qualities are the whole game. A longer, more even filament means fewer weak points and a cloth that wears for years rather than months. Its natural paleness means it takes colour cleanly and truly. And gram for gram, silk is one of the strongest natural fibres there is, which is a quiet marvel for something that feels like air.

The smoothness is the part you actually feel. A mulberry silk surface creates very little friction, which is why it sits so kindly against skin and hair through the night where cotton tugs and creases. It's also naturally breathable and tightly woven, qualities that make good silk gentle on sensitive skin.

Mulberry silk versus other silks

The main alternative is wild silk, usually sold as tussah, spun by moths that feed on oak and other leaves out in the open. It's coarser, shorter in the staple, and a natural tan-brown that can't be bleached to a clean white. Lovely for a rustic, textured wrap. Less lovely against your cheek at 2am. There are others too, like eri and muga, each with their own character.

One thing worth clearing up: “eucalyptus silk” and “bamboo silk” aren't silk at all. They're lyocell — a plant fibre given a silky finish. Often perfectly nice, but a different thing entirely, and worth knowing when you're comparing a price.

The two numbers that tell you if silk is good: momme and grade

Silk quality comes down to two small things, and you genuinely need both. The first is momme (say it MOH-mee), the measure of how dense and heavy the weave is. For a pillowcase, 22 momme is the sweet spot — substantial enough to last under regular washing, still soft enough to feel like a treat. The second is grade, which describes the raw fibre's length and consistency, running from 6A at the top down through lesser letters. 6A is the longest, finest and most even.

Here's the catch most shops won't tell you: a high momme woven from low-grade fibre still disappoints, and a beautiful grade woven too thin won't last. You want both. Every LS Silk pillowcase is 22-momme, 6A-grade, 100% mulberry silk — which is simply the honest combination that holds up.

Is mulberry silk really better for skin and hair?

Yes, and for one plain, physical reason: it's smooth. Less friction means less of the tugging and creasing that leaves sleep lines on your face and frizz in your hair by morning. Because silk is also less absorbent than cotton, it leaves your skin's moisture and your night creams where they belong rather than drinking them up. None of it is magic. It's just a kinder surface to spend a third of your life against. We've written more on the why silk is better for hair and skin if you'd like the detail.

How to keep mulberry silk beautiful

Looked after gently, mulberry silk lasts for years — and looking after it is far easier than its reputation suggests. Cool water, a gentle hand, a mild wash, and a spot out of direct sun to dry flat. That's most of it. The protein that makes silk so lovely is the same protein that dislikes heat, harsh detergent and hard sunlight, so the whole of silk care follows from understanding what it actually is. Our silk care guide walks through it step by step.

If you're ready to feel the difference for yourself, our 22-momme mulberry silk pillowcases are where most people begin.

There's a neat symmetry to it, really. A fibre this refined comes down to one small caterpillar, fed one kind of leaf, with great patience, for five thousand years. Understand that, and everything else about silk — the price, the feel, the care — quietly makes sense.