If you have shopped for silk lately, you have run into a small number printed next to almost everything. 19 momme. 22 momme. Sometimes 25 or 30. It sits there like it means something obvious, and nobody stops to explain it, so most of us nod along and quietly assume that bigger must be better.
It is not quite that simple, and the difference between the two most common weights, 19 and 22, is worth understanding before you spend money. Not because one is good and the other is bad. They are both real silk. They just do different jobs, and knowing which is which saves you from either overpaying for weight you will not feel or underpaying for a piece that thins out in a year.
So let us walk through it together, plainly, and by the end you will know exactly what that little number is telling you.
What Momme Actually Measures
Momme, pronounced roughly like "mummy" and written as "mm," is an old Japanese unit for the weight of silk. The technical definition is a mouthful: it is the weight in pounds of a piece of silk that measures 45 inches wide and 100 yards long. If that bolt of fabric weighs 19 pounds, the silk is 19 momme. If it weighs 22, it is 22 momme.
You do not need to memorize that. Here is the part that matters. Momme measures how much silk is actually in the fabric. A higher number means more silk threads packed into the same space, which means a heavier, denser cloth. It is a measure of substance, not of quality on its own. A beautifully made 19 momme and a poorly made 22 momme are entirely possible.
One thing worth clearing up while we are here, because the words get used interchangeably and they should not be. Momme is the weight. Mulberry is the fiber. Momme tells you how heavy the silk is, mulberry tells you what kind of silkworm produced it. A piece can be 22 momme and not be mulberry silk at all. When you see "100% mulberry silk, 22 momme," you are being told two separate facts, and both are worth having.
The Real Difference Between 19 and 22
Twenty-two momme has roughly fifteen percent more silk in it than nineteen momme, by weight. In grams per square meter, 19 momme lands around 82 and 22 momme around 95 to 100. That is not a dramatic gap on paper. In your hands it is noticeable.
Here is what that extra silk changes.
Weight and drape
Nineteen momme is light. It moves with you, floats a little, feels cool against warm skin, and settles softly rather than falling in heavy lines. Twenty-two momme has more presence. It hangs closer to the body, drapes in fuller folds, and holds its shape instead of drifting. If you have ever picked up a robe that felt like it was made of water and another that felt like it had real substance, that difference is often momme.
Opacity
More silk means less light passes through. Nineteen momme can be slightly sheer depending on color and construction. Twenty-two momme is more opaque and reads as more substantial. For some pieces that matters a great deal, and for others it does not matter at all.
Durability
This is the honest headline. The extra density in 22 momme gives it more to give. It resists the friction of nightly movement and regular washing better than a lighter weight, and it tends to show wear more slowly. Well made and well cared for, heavier silk can last for many years without thinning or pilling. Nineteen momme is perfectly durable too, especially for a garment that is not handled roughly. It simply has a little less margin.
Cost
All of the above is why 22 momme costs more. There is no trick to it. A heavier weight uses more raw silk to make the same garment, and raw silk is the expensive part. Across the market, a step up from 19 to 22 momme usually adds somewhere in the range of fifteen to twenty percent to the price. You are not paying for a label. You are paying for more of the actual material.
So Is Heavier Always Better? No.
This is where a lot of silk marketing quietly loses the plot, and I would rather be straight with you.
Higher momme is not a quality ladder you are supposed to climb as high as your budget allows. Past a point, the returns flatten out fast. The jump from 19 to 22 is meaningful and easy to feel. The jump from 22 to 25 is marginal for most people, and above that you are mostly buying weight for its own sake, which can actually work against a garment that is supposed to feel light and breathe.
For sleepwear specifically, the sweet spot sits right in the 19 to 22 range. That is not a compromise. That is the range where silk does what we actually want it to do at night, which is feel cool, breathe, move easily, and last.
The right question is not "what is the highest number I can get." It is "what is this particular piece for."
Matching the Weight to the Job
The cleanest way to think about it is to ask what the garment has to do.
A piece worn directly against your skin all night, like a nightgown or a slip, benefits from being lighter. You want it cool, soft, and weightless, something you stop noticing the moment you lie down. Nineteen momme is lovely for exactly this. It breathes, it drifts, it does not cling or warm you up, and because it is not taking much friction from the outside world, its slightly lower durability is rarely an issue.
A piece worn as an outer layer, like a robe, is doing a different job. It is handled more. You tie it, untie it, throw it over your shoulders, catch it on doorknobs, wash it more often because it lives on the outside. It also wants structure. A robe that drapes with a bit of weight looks and feels far more considered than one that hangs limp. This is precisely where 22 momme earns its keep. The extra substance gives it drape, it holds its shape through years of tying and washing, and the added durability actually matters because the garment lives a harder life.
This is not theory for us. Our silk night dress is 19 momme, chosen deliberately so it stays cool and light against your skin through the night. Our robe is 22 momme, chosen just as deliberately because a robe should have weight, should drape properly, and should survive being lived in. Two pieces, two weights, two jobs. The robe costs more partly because there is simply more silk in it, and now you know exactly what that means rather than having to take our word for it.
What to Actually Look For When You Shop
You do not need to become an expert. A few habits will carry you.
Look for the momme number stated plainly. A brand that is proud of its silk will tell you the weight without being asked. If a listing describes silk as "premium" or "luxury" but never names a momme, that is worth a raised eyebrow. It might still be good silk. You just cannot tell, and you deserve to be able to tell.
Match the weight to the use, not to your wallet. For something against your skin all night, lighter is often the smarter buy. For an outer layer that needs to drape and last, the heavier weight is usually worth it. Buying up to 25 or 30 momme for a nightgown is often paying for weight you will actively wish was not there.
Check that momme and fiber are both disclosed. "22 momme, 100% mulberry silk" tells you the weight and the fiber. "22 momme silk" alone tells you only half the story.
And if you want to know how a brand tests or certifies its silk, ask. A good one will answer quickly and specifically. How someone responds to a fair question tells you a great deal.
The Short Version
Momme is just a measure of how much silk is in the fabric. Twenty-two momme costs more than 19 because it contains more silk, roughly fifteen percent more by weight, and that extra material buys you a fuller drape, more opacity, and better durability. That is real value, but only when the garment's job calls for it.
Heavier is not automatically better. It is better for pieces that need weight and take wear, like a robe, and unnecessary for pieces meant to feel light and cool against your skin, like a nightgown. The 19 to 22 range is the honest sweet spot for sleepwear, and above it the gains get small fast.
So the next time that little number turns up on a label, you will not have to guess. You will know what it measures, what you are paying for, and whether this particular piece actually needs it. That is the whole point. Not to spend more, but to spend on purpose.
By Ann Havenly
MoonThreads makes sleepwear from GOTS-certified organic cotton and OEKO-TEX Standard 100 certified 100% 6A grade mulberry silk. Certificate numbers available on request.