What does momme mean? 19, 22 and 25 momme explained

Momme is the weight of a silk fabric. It tells you how much silk sits in each square metre, and nothing more. When you are comparing silk pillowcases it is a useful number, as long as you know what it can and cannot tell you.

What is momme in silk?

Momme, often written mm, is a unit of weight for silk fabric. One momme is 4.34 grams per square metre (Store norske leksikon). So a label that reads 22 momme, or 22 mm, is telling you how heavy the fabric is for its size.

That is all it measures. Momme does not rate the fibre, the weave or how well the fabric was made. More momme means more silk per square metre, so a denser, heavier fabric. That is the whole of it.

How heavy are 19, 22 and 25 momme silk?

Because one momme is a fixed weight, the sums are simple. Worked out from the 4.34 g figure:

• 19 momme is about 82.5 g of silk per square metre.
• 22 momme is about 95.5 g per square metre.
• 25 momme is about 108.5 g per square metre.
• 30 momme is about 130.2 g per square metre.

So a 25 momme fabric carries more silk than a 19 momme one of the same size, and it is denser and heavier. That difference is real. What it means for you is a different question.

Is a higher momme silk better?

It is heavier. No study shows it is better for your hair or skin. Momme is not a grade of fibre quality, and we found no study showing that a particular momme gives better results for hair or skin. If you read that each extra momme does more for you overnight, it is fair to ask what that is based on.

The same goes for how long a pillowcase lasts. It is tempting to assume more silk means a longer life, but we found no study of silk pillowcase lifespan at any momme, so we will not put a number of years on one. What is documented is care. Strong alkaline detergents weaken silk and sunlight fades it, so wash cool with a pH-neutral detergent without enzymes or bleach, skip the tumble dryer and dry it out of direct sun. Our care guide has the details.

Our own pillowcase is 22 momme, 100% mulberry silk. We are not going to tell you 22 is the right number for your hair or skin, because no study shows that any momme is. It is a weight, and we would rather tell you exactly what it means than dress it up. We take the same line on the bigger claims, which is why our honest look at sleep lines says what it says.

What does momme not tell you?

Momme is one line on a label. Here is what it leaves out.

• The fibre. Satin is a weave, not a fibre, and most low-cost satin pillowcases are polyester. Look for the fibre content on the label. There is more on this in silk vs satin.
• The weave. Charmeuse is a satin weave with long floats on the face, which gives a glossy front and a dull back. It can be woven from silk, polyester or rayon, so "charmeuse" on its own does not mean silk.
• The grade. Grades such as 6A rate raw silk yarn under China's grading standard, and the grade is set by the yarn's lowest test score. A grade rates the yarn, not the finished pillowcase, and there is no 7A or higher.
• Safety testing. OEKO-TEX Standard 100 is a label for textiles tested for harmful substances, and a certificate can be checked by its number on the OEKO-TEX site. It is not an organic, ethical or environmental label.

Mulberry silk itself is reeled as one continuous filament from the cocoon, so there are no short fibre ends on the surface. Short-fibre spun silk is made more like cotton yarn. Momme will not tell you which of the two you have either.

How can you check a momme claim?

A momme figure is a weight, so it can be weighed. The proper check is a fabric mass test, which measures mass per unit area under ISO 3801. For a grade, the equivalent is the raw silk inspection certificate, not a sales sheet that simply says 6A. If a seller quotes either, it is fair to ask how they know.

Our science page sets out what we have read on momme, grade and certificates, with sources, and the FAQ covers the basics in a line or two.