What is momme in silk?

Momme is inherited from the Japanese measurement of silk. It corresponds to the weight of a piece of fabric of conventional dimensions: historically, the weight in pounds of a piece 100 yards long and 45 inches wide.

It is a traditional unit, not a modern metrological standard. It has survived because it is practical: it gives a simple figure, comparable from one manufacturer to another, where grams per square metre are little used in the silk trade.

Not all silks are intended for the same use, and weights are graded accordingly.

These conversions are orders of magnitude: the exact figure varies slightly with each manufacturer's conventions.

It answers a single question, but it answers it well: is this fabric denser than that one?

That density has observable consequences. A heavier fabric is more opaque, drapes more heavily, and presents a tighter surface of fibres to daily friction. At comparable thread quality, it withstands the wear of repeated night-time use better.

This is why 16 momme is poorly suited to a pillowcase: the fabric is thin, it marks sooner and copes less well with repeated washing.

This is where many product pages take liberties.

1. It says nothing about thread quality. Two silks of the same weight can be woven from very different threads: filament length, regularity, number of breaks. A poorly spun 22 momme will feel worse than a well spun 19 momme.

2. It says nothing about the type of silk. A tussah and a mulberry silk can show the same momme and share neither feel nor appearance. Weight is always read alongside composition.

3. It says nothing about the finishing. Seams, closure, hems: none of that appears in the weight. Yet seams often give way before the fabric does.

This is the most widespread shortcut, and it is wrong.

Increasing the weight thickens the fabric. A thicker fabric is stiffer, drapes less softly, and costs more — the price of silk is directly tied to the weight of material. Past a certain point you are paying for a density that adds nothing to the use of a pillowcase, and that can even work against the drape.

Momme is therefore a trade-off dial: enough density to last, enough suppleness to follow the pillow. That is why 22 has become the most common value for pillowcases, and it is the weight we chose.

A buyer cannot measure momme at home without a precision scale. What they can do is spot the signs of a doubtful figure.

• A weight stated without a composition. “25 momme” without “100% mulberry silk” means nothing.
• A high weight at a very low price. Material has a cost; a 25 momme pillowcase at £20 is an arithmetical improbability.
• Unusual round numbers. Commercial weights cluster around a few values. A “40 momme” pillowcase deserves questions.

Are momme and thread count the same thing?

No. Thread count counts threads over a given length and is used for cotton. Momme weighs the fabric. The two are not convertible.

What momme should I choose for a pillowcase?

Between 19 and 25 depending on budget and the finish you want. Below 19 the fabric wears faster; above 25 you are mostly paying for weight.

Does a higher momme make the pillowcase smoother?

Not directly. The sensation of glide comes from the weave and the regularity of the thread, not from the weight. A denser fabric is more opaque and heavier, which is not the same as smoother.

Does momme change after washing?

The weight of the fabric does not change. What changes is the condition of the fibres: a wash that is too hot, or an enzyme detergent, attacks the surface and alters the feel without greatly changing the weight.

Weight is only one criterion out of six: see our guide to choosing a silk pillowcase. And if the original question was how to tell silk from a synthetic satin, the answer is in silk or satin.