What 6A, 22 Momme Silk Really Means on a Slip Pillowcase

It's 11 p.m., I'm at the bathroom sink with a layer of night cream still tacky on my cheeks, and I'm holding my phone with the Slip pillowcase in charcoal, queen, envelope closure pulled up. The spec line reads 6A long-fiber mulberry silk, 22 momme. Two numbers sitting side by side, and most people read them as the same kind of number — a score, higher is better, better means better skin.

They're not the same kind of number. 6A grades the raw silk filament before it ever reaches a loom. 22 momme describes the finished cloth you actually press your face into. And the laboratory line further down the page claims only that the pillowcase pulls less face cream out of your skin than cotton does — one comparison, one measured quantity, no skin involved at all. The number you're really paying for is the 22.

What 6A and 22 momme actually specify

Momme is a weight, and specifically a weight per area: one momme equals 3.75 grams per square meter, so a 22-momme silk runs about 82.5 g/m². That's a dense, slightly heavy cloth — you feel it hang when you lift the case out of the box, and it creases less than the thin stuff. The brand's own wording is that Slipsilk is 100% pure mulberry silk, commissioned and made to Slip's standards, developed and refined over ten years to combine shine, thickness, softness and durability. The thickness in that sentence is the 22.

6A measures something else entirely. It grades raw silk filament — how long and how even the individual fibers are, scored 2A through 6A after degumming and reeling, before any weaving happens. Slip says it buys the highest grade, 6A long fiber, 100% pure mulberry silk, 22 momme, dyed with non-toxic dyes under the strictest quality guidelines it can enforce. Here's the part buyers miss: a 6A filament can be woven into a 19-momme case or a 30-momme case, and the grade stays honest in both while the drape, the feel and the lifespan come out completely different. A customer of mine who sells bedding online — side sleeper, heavy retinol user — asked me whether 6A or 30 momme was the better buy. The gram weight is the number that carries the wear; the letter is a claim about the fiber that was delivered to the loom.

How 22 momme differs from thinner silk and satin

Most silk pillowcases retail between 16 and 19 momme, and 19 is the number you'll see most often. Twenty-two sits above that band. The difference isn't vanity. A 16-momme charmeuse goes slightly see-through against a bright window, and the place it fails first is the hem, the folded and stitched edge where two layers rub through seven or eight washings and start to bloom into fuzz. The body of the cloth pills where your ear and jaw drag across it nightly. A 22-momme weave puts roughly a third more silk into every square meter, so the same abrasion eats fewer fibers per pass; the hem holds, the surface stays smooth, and you aren't replacing the case in eighteen months.

The other thing sitting next to it on the shelf is satin. Satin is a weave structure, not a fiber, and it can be polyester — the fifteen-dollar polyester satin cases look and feel close to silk for the first ten seconds you hold them. What's missing is the protein fiber and the breathability. Polyester traps heat, and a hot sleeper feels that by 3 a.m. The word satin on a listing tells you nothing about what you're buying. 100% mulberry silk does.

What the face-cream lab test actually compared

Now the sentence that sells the pillowcase to half the people who buy it. Slip states that in laboratory testing, slipsilk pillowcases absorbed significantly less face cream than cotton pillowcases, so they help keep your skin's moisture and your face and hair products where they belong, on your face and hair. Read what that actually compares: silk against cotton. Two materials, one measured quantity, cream absorbed. There's no number attached, no description of the method, and no measurement of anything on a person — no skin hydration, no water loss, no hair breakage count. It's a materials comparison dressed up as a beauty claim.

The obvious objection is the one every skeptic lands on: the brand paid for the test, and cotton is the easiest opponent in the drawer. Cotton is hydrophilic, which is exactly why it makes good towels; the fiber swells with water and holds it. Of course it drinks more cream than silk. A fairer comparison would have been against the polyester satin going for a sixth of the price, and Slip didn't run that one. The second half of the objection is subtler and harder to wave off: cream sitting on the surface of a fabric is not the same as cream staying on your skin, and a case that doesn't absorb the cream still lets you roll your cheek across it for eight hours.

Why the weave matters if you sleep on your side

Which brings up the second challenge, and it's a good one. A skeptic would say the cream is mostly gone by morning anyway — some soaks in, some transfers to the pillow, some rubs off on the sheet — so a few extra grams left on the fabric changes nothing, and nobody has measured whether a silk pillowcase raises skin moisture at all. Fair. The evidence doesn't show your skin getting better, and anyone selling that is overselling. The narrower claim, though, survives scrutiny.

Behind that sits a mechanical argument that does hold. Lie on your side under a heavy night cream with a cotton case, and by the end of the week the cotton carries a visible oil shadow where your cheek rested, a mark that survives the wash. The cream went into the fiber. Silk's smooth filament surface has far less of the microscopic scale and loft that grabs and holds a cream, so more of it stays on the skin side of the contact. The 22-momme weight and the non-toxic dye process matter here too: a denser, better-finished weave keeps its smooth face longer, so the property you're paying for doesn't wear off in the first year. Nobody has run the skin-moisture study. The product-loss effect is real, and it's the one that shows up on your face every night.

How to check the tag, and whether it's worth buying

If you're going to spend the money, check the tag the way you'd check a thread count. Find the momme number in the spec table, not the headline — 22 momme, sometimes written 22mm — because that's what decides how the case survives the wash. Look for 100% mulberry silk rather than satin, which as covered can be polyester. Read the care line as well, since you're protecting exactly the layer you paid for: neutral detergent, no bleach, no hot dryer, dry in the shade. A pillowcase that goes through a hot dryer every week loses the finish that made it worth having.

Back to the doubt you're probably still holding. The test was the brand's own, cotton was a soft target, and none of that says your skin will improve. That doesn't settle the question by itself. If you sleep on your side, use thick creams, and are tired of finding your product soaked into the pillow instead of sitting on your face, buy it — buy it for the 22-momme weave and the years of washing it will take, and treat the lab line as a supporting detail rather than the reason. If what you want is proof of a skincare result, keep your money, because nothing here supports that, and no pillow is going to do the job your serum is supposed to do.