What is mulberry silk, and why is it reeled not spun?

Mulberry silk is silk from silkworms that feed on mulberry leaves. What sets it apart is how the thread is made. It is reeled from the cocoon as one continuous filament, rather than spun from short fibres. Here is what that means, what the fibre is made of, and what the word "mulberry" on a label does and does not tell you.

What is mulberry silk?

Each silkworm spins a cocoon, and the silk comes from that cocoon. Mulberry silk is the name for silk from silkworms fed on mulberry leaves.

Silk is a natural protein fibre. That puts it in a different family from polyester, which is made from fossil fuels. One measured difference shows it well. In standard conditions silk takes up about 11% of its weight in moisture from the air. Polyester takes up 0.4 to 0.8%. We explain that figure in does silk absorb less moisture than cotton?

"Mulberry" on a label tells you where the silk came from. It does not tell you the weight of the fabric, the grade of the yarn or how it was woven. Those are separate things, and we come to them below.

What does reeled silk mean?

Reeling is how the silk comes off the cocoon. Mulberry silk is reeled as a single continuous filament, unwound from the cocoon in one long length.

Because the filament runs unbroken, there are no short fibre ends on the surface of the yarn. That is one reason a reeled silk fabric feels smooth. The weave is the other reason, and it matters just as much.

A label that says long-fibre or filament silk is describing reeled silk. On a pillowcase, woven well, it gives your hair a smooth surface to move across while you sleep.

What is spun silk, and how is it different?

Spun silk is made from short silk fibres, in much the same way as cotton yarn. Because it starts as short lengths, it does not have the unbroken filament of reeled silk.

The word "spun" can be confusing here. Silkworms spin their cocoons, so in one sense all silk is spun. When people talk about spun silk yarn, though, they mean yarn made from short fibres. Reeled silk is yarn made from the continuous filament.

Most peace silk is spun. In peace silk the moth leaves the cocoon first. A broken cocoon cannot be reeled, so the silk is made into spun yarn instead.

What is silk made of?

Raw silk is two proteins. Fibroin is the fibre itself. Sericin is the gum that holds the strands together, and it makes up about 25 to 30% of the protein in raw silk.

Before silk is woven into a smooth fabric like charmeuse, the sericin is washed out in a process called degumming. So a finished silk fabric of that kind is mostly fibroin. Our science page sets this out with its sources.

It is also why care advice for silk is gentle. You are washing a protein fibre, and strong alkaline detergents weaken silk. A pH-neutral detergent with no enzymes or bleach is the usual advice. We go through it step by step in how to wash a silk pillowcase.

Do silk proteins do anything for your skin?

You may read that silk's 18 amino acids nourish your skin, or that sericin hydrates it, but no study has shown either. We found no study showing amino acids moving from a silk pillowcase into skin, and fibroin is an insoluble fibre.

Sericin has been tested in creams put on the skin. A cream is a different thing from a fabric. In a smooth silk fabric like charmeuse, the sericin has already been washed out in degumming.

So we describe silk as what it is: a natural protein fibre, made mostly of fibroin. Skin claims about silk proteins are on our list of claims we don't make.

What should you look for on a mulberry silk label?

"100% mulberry silk" tells you the fibre. A few other words tell you about the fabric made from it.

• Momme is a weight. 1 momme is 4.34 g per square metre, so 22 momme is about 95.5 g/m². A higher momme means a denser fabric. It is not a grade of quality. More in what does momme mean?
• Grade 6A is the top grade for raw silk yarn under China's grading standard. It rates the yarn, not the finished pillowcase, and there is no 7A or higher grade. A grade means most when there is a raw silk inspection certificate behind it.
• Charmeuse is a satin weave. Threads float over several cross threads on the face, giving a glossy surface and a dull back. It can be woven from silk, polyester or rayon, so charmeuse alone does not mean silk.
• OEKO-TEX Standard 100 is a label for textiles tested for harmful substances. Certificates can be checked by number on the OEKO-TEX site. It is not an organic or environmental label.

Satin is the word to watch. It is a weave, not a fibre, and most low-cost satin pillowcases are polyester. We compare the two in silk vs satin pillowcases, and the silk questions on our FAQ cover the basics.

SOIEA is 100% mulberry silk at 22 momme, in champagne and blush, launching in December 2026 for the UK and Ireland. See the pillowcase.