What Is Silk? Mulberry Silk, Wild Silk and Momme Weight

Silk is one of the few materials people buy by name without knowing much about it. It is understood to be luxurious and delicate, and that is roughly where most descriptions stop. The material itself is more specific than that, and the specifics are what explain how it behaves against skin, in a wardrobe, and in a wash basin.

Below: what silk actually is and how it is made, how mulberry silk differs from wild and from spun silk, what the momme number measures and which weights suit a scarf, what a 6A grade covers, what an OEKO-TEX certificate tests, what the word hypoallergenic can honestly be said to describe, and how to read all of that off a label.

What Silk Is

Silk is a protein fibre. That single fact separates it from almost everything else in a wardrobe: cotton, linen and viscose are cellulose, polyester and nylon are plastics, and only silk and the animal hairs — wool, cashmere, mohair, alpaca — are proteins.

The protein in silk is called fibroin. A silkworm produces it as a liquid and extrudes two continuous strands, binding them together with a second protein, sericin, which sets on contact with air and works as a gum. That is the cocoon. Most of the sericin is washed out afterwards in a stage called degumming, which is what turns a stiff, dull thread into the soft, light-catching fibre people recognise as silk.

The property that matters most is that the fibre is continuous. A single cocoon can be unwound into one unbroken filament hundreds of metres long. Cotton and wool cannot do this. They are staple fibres, short lengths that have to be twisted together into yarn, which leaves fibre ends protruding along the entire surface of the thread. A reeled silk filament has almost none. Nearly everything else silk does follows from that one structural difference.

Mulberry Silk and Wild Silk

"Silk" is not a single material. The distinction worth knowing first is between cultivated and wild silk.

Mulberry silk

Bombyx mori is a moth domesticated so long ago that it no longer exists in the wild and can no longer fly. Its larvae are reared indoors and fed one food: the leaves of the white mulberry tree. That is where the name comes from. Mulberry silk is silk from worms raised on mulberry leaves, not a grade and not a brand.

A controlled diet under controlled conditions produces a controlled fibre. Mulberry cocoons are near-white and consistent in size, and they can be reeled off in one long continuous filament. The yarn that results is even in diameter, smooth along its length, pale enough to dye cleanly to any colour, and strong for its weight.

Wild silk

Wild silks come from moth species that were never domesticated. Tussah, from Antheraea species, is the most common, alongside eri and muga. These larvae feed in the open on oak, arjun, castor and other leaves, and their diet varies from cocoon to cocoon. So does the fibre.

Wild cocoons are often collected after the moth has emerged, which breaks the filament, and broken filament cannot be reeled: it has to be cut to short lengths and spun into yarn, much like wool. This is not a rule for the whole group — muga is reeled commercially and some tussah is too, while eri is always spun — but spun yarn is what most wild silk on the market is. The consequences follow directly:

• Short fibres spun together, so the yarn surface carries protruding ends
• Irregular diameter, which reads as slubs and texture in the finished cloth
• A drier, coarser hand, closer to a fine linen than to a mulberry satin
• Natural tan and gold tones that resist even, predictable dyeing

None of that makes wild silk inferior. Tussah has a character mulberry silk cannot imitate, and it is chosen deliberately for textured weaves and undyed cloth. But it is a different material that behaves differently, and it is the smooth, uniform, reeled filament rather than silk in general that everything below rests on.

What Separates Mulberry Silk from Ordinary Silk

A label reading "100% silk" is a statement about fibre content and nothing else. It is accurate, it is regulated, and it covers every silk described above equally: reeled mulberry filament, spun tussah, and the short broken fibre left over from reeling. Those three do not cost the same, do not feel the same and do not wear the same. Naming mulberry silk narrows it, and four things change when it does.

• The species and the diet are fixed. Mulberry silk is Bombyx mori, reared indoors on white mulberry leaves. Ordinary silk may be any species that spun a cocoon on any tree. A controlled input is the only reason the output repeats from batch to batch.
• The filament is reeled rather than spun. An intact mulberry cocoon unwinds in one piece. That is the difference between a thread with almost no fibre ends on its surface and a thread covered in them, and it is what produces the sheen. Sheen is a surface effect, not a coating, so it does not wash off.
• The colour starts near-white. Wild cocoons carry their own tan and gold. Mulberry silk takes a dye to the colour that was specified, which matters most for printed designs where a shifted base colour shifts everything printed on it.
• The diameter is even. Consistent filament thickness is what allows a fine, flat, dense weave. Irregular yarn gives slubs, and slubs are a feature in a rustic cloth and a fault in a printed scarf.

One thing hides inside an entirely correct silk label, and one gets mistaken for silk altogether. Spun silk, sold as noil, bourette or schappe, is made from the short broken fibre that cannot be reeled, including the waste from reeling mulberry cocoons. It is genuinely 100% silk and can genuinely be mulberry silk, but it is spun from staple, so it has a matte, slightly fuzzy surface rather than the smoothness people are usually paying for. And "art silk" or "artificial silk" is not silk: it is viscose rayon, a cellulose fibre made from wood pulp. It belongs in the same family as cotton, not in this article.

Momme: What the Weight Number Means

Momme is the traditional weight measure for silk. It is abbreviated mm, which has nothing to do with millimetres and causes endless confusion. One momme is the weight in pounds of a piece of that silk cut 45 inches wide and 100 yards long. It is an awkward definition, and the useful way to hold it is the conversion: one momme is about 4.3 grams per square metre. So 14 momme is roughly 60 g/m² and 18 momme roughly 77 g/m².

Momme measures how much silk is in the cloth. That is all it measures. It is a quantity, not a verdict.

The range in practice

Silk is woven across a very wide weight band, and the name of the weave usually implies where in that band it sits:

• Gauze and organza, 3 to 6 momme — sheer and crisp, used for structure more often than for scarves
• Chiffon, 6 to 8 momme — transparent
• Habotai, 5 to 16 momme — a thin lining silk at the bottom of that range and a substantial cloth at the top
• Crepe de Chine, 12 to 16 momme
• Charmeuse, 12 to 30 momme — the top of that range is heavy bedding and furnishing, not something anyone wears at the neck

Printed silk scarves in practice sit somewhere between about 8 and 19 momme. Below 8 the cloth is sheer enough that the design shows through to the reverse and the scarf has no weight to hang with. Above 19 it stops behaving like a scarf: it resists folding, stands away from the neck, and a knot in it reads as a knot in a tie. Within that band, 12 to 16 momme is where most silk meant to be worn rather than displayed actually sits.

So are 14 and 18 momme good weights?

Yes, both of them, and for different reasons. Stated plainly rather than hedged:

14 momme, about 60 g/m², is the middle of the scarf range and the middle of the crepe de chine band. On a 90 × 90 cm square that is the weight that separates a scarf which drapes from one which floats — enough body to fall in a defined line and hold a knot, not so much that the square turns stiff and refuses to fold down small. Going heavier on a piece that size is not an upgrade. A 90 × 90 square at 20 momme is a genuinely awkward thing to wear, and the extra material makes it worse rather than better. 14 momme on a large square is a choice, not a saving.

18 momme, about 77 g/m², is heavy for a scarf. It sits above the crepe de chine band entirely, in the weight range where charmeuse is usually woven, and on a large square it would be too much. On a ribbon scarf it is exactly right, for a reason that is specific to the shape: the piece is 85 × 5 cm, and a narrow strip has almost no self-weight to work with. At a light momme a ribbon scarf collapses, twists along its length and will not hold a knot on a bag handle or at the base of a ponytail. The extra weight is what keeps it a defined ribbon rather than a piece of string.

The caveat is the one that applies to the unit itself. Momme cannot tell you whether a silk was woven well, printed well or finished well, and a heavy silk can fail at all three. What it does tell you reliably is whether the cloth has been thinned to save money. At 14 and 18 momme it has not.

Silk Grades and What 6A Means

Raw reeled silk is classified before it ever reaches a loom. The scale runs 6A, 5A, 4A, 3A, 2A, A and then lettered grades below that, with 6A at the top. What is being graded is the reeled yarn: how even the filament is along its length, how far its thickness deviates from nominal, how clean it is of neps, loops and slugs, and how consistently it runs. It is a commercial classification used within the silk trade and applied by the producer of the yarn, rather than a consumer label or an independent audit.

CIATAU's fabrics are woven from 6A mulberry silk, which is what the fabric supplier certifies, and which is the top of that scale.

It is worth being precise about what that covers, because it is narrower than it sounds. A grade describes the thread going into the loom. It says nothing about the weave, the print, the dye or the finish, and between them those decide most of what a finished scarf looks like and how it survives being worn. A 6A yarn woven and finished carelessly still makes a poor scarf. The grade is a floor under the raw material rather than a description of the object made from it.

OEKO-TEX STANDARD 100

CIATAU holds an OEKO-TEX STANDARD 100 certificate for its silk fabrics.

The standard is a testing scheme. An accredited institute tests the submitted material, and the components attached to it where those form part of the certified article, against a criteria catalogue of specified harmful substances, each with a defined limit value. The catalogue is assembled from regulated substance lists — the REACH restricted substances annex and the European Chemicals Agency candidate list among them — plus substances that are not yet regulated anywhere. Requirements tighten according to how much skin contact the product class implies. Certification means the tested material came in under those limits.

That is the whole of the claim, and it is worth saying what sits outside it. It is a chemical-residue test on a material. It is not a rating of quality, weave or durability, it is not a statement about how any individual person will respond to a textile, and it is not a health claim. It also has a shelf life: STANDARD 100 certificates are issued for a year and have to be renewed, so the only certificate worth anything is a current one.

What "Hypoallergenic" Is Describing

"Hypoallergenic" is a conclusion. The properties it is drawn from are the part worth looking at, because those are the things that can actually be described.

The surface holds less

Household allergens are largely particulate: dust, pollen, pet dander, shed skin. Fabrics collect them mechanically, on whatever surface area and protruding fibre ends they present. A napped wool or a brushed cotton offers a great deal of both. A smooth, tightly woven filament silk offers very little, and it does not fibrillate, meaning it does not break down into fine surface fuzz with wear the way a spun staple yarn does. Less to catch on, less retained, and what does settle is shaken off more readily.

It is a poor habitat for dust mites

Dust mites need two things from a textile: a food supply of shed skin, and enough trapped humidity to survive. They colonise deep, lofty, moisture-holding materials well and dense smooth ones badly. Silk takes up moisture readily but gives it back to the air quickly rather than holding it, and a tightly woven silk offers very little depth to settle into. That makes it an inhospitable surface, not an impossible one. The property is about how poorly the material suits mites, not about eliminating them.

It resists mould

Mould needs sustained damp. Silk's moisture behaviour works against that: it absorbs humidity and releases it back quickly, so in ordinary use it does not stay wet. This describes the material in normal conditions and is not a licence to ignore it. Silk stored damp, or sealed in plastic, will mildew like anything else, which is why the care guide asks for a breathable bag rather than a plastic one.

Where the claim stops

"Hypoallergenic" has no legal definition in textiles. It is a comparative description of a material, not a certification and not a health claim, and the structure of a fibre says nothing about how any individual will respond to it. Silk is itself a protein, and dyes and finishes are a separate variable again. The accurate version of the claim is narrow, and worth stating plainly: silk's smooth, continuous-filament structure traps less dust and dander than napped or spun fibres, offers dust mites a poor habitat, and resists mould. Everything past that is inference, and is better labelled as such.

Reading a Silk Label

Put all of that together and a composition label reading "100% silk" tells you exactly one thing: the fibre is silk and there is nothing else in it. It does not tell you the species, whether the yarn was reeled or spun, what the cloth weighs, how the yarn graded, or whether the finished material has been tested for anything at all. Those are five separate questions, and most sellers answer none of them.

What CIATAU's Silk Is

In those same five terms:

• Fibre — 100% mulberry silk, produced by Bombyx mori, with no other fibres blended in
• Construction — woven, not knitted and not spun from staple
• Weight — 14 momme for the large square scarves, 18 momme for the ribbon scarves
• Grade — 6A mulberry silk, as certified by the fabric supplier
• Testing — OEKO-TEX STANDARD 100 certified fabrics

The large scarves measure 90 × 90 cm and the ribbon scarves measure 85 × 5 cm. Every pattern is drawn in Lithuania and every scarf is finished there. The silk itself is woven abroad, which is why the scarves are described as designed in Lithuania and not as anything more than that.

More on looking after it in the silk care guide, or see the full CIATAU silk scarf collection.