Thread Count, GSM and Momme: How to Actually Read a Fabric Spec

Every fabric on a bedding site comes with a number attached, and almost nobody explains what the number measures. Worse, the three numbers you will meet — thread count, GSM and momme — are not interchangeable, and one of them has been so thoroughly abused by marketing departments that it is close to meaningless on its own.

Here is what each one actually tells you, and what it does not.

Thread count: useful up to a point, then a lie

Thread count is the number of threads woven into a given area of fabric — warp (lengthways) plus weft (crossways). More threads in the same space means a denser, smoother, generally more durable cloth. That much is real.

The problem is that thread count can be inflated. A manufacturer can twist several thin, weaker plies together, count each ply separately, and quote 800 or 1,000 on a fabric that is objectively worse than an honest 300 made from single, longer, stronger yarns. This is why a supermarket "1000 thread count" set can feel heavy, hot and lifeless while a good 300 feels superb.

The rule: above roughly 400, treat thread count as marketing until proven otherwise. Below that, it is a reasonable proxy for density — and fibre quality matters more than the number either way.

The unit trap nobody mentions

There is a second problem: thread count is not always quoted in the same unit. American brands almost always quote threads per square inch. European and Asian mills often quote threads per 10 square centimetres, which produces a much larger-looking figure for the same cloth.

Our Silky Cotton is specified at 300 thread count, in threads per square inch — the same unit we use for Cloud Cotton and Plain Cotton, so the three figures compare directly. That is a genuinely dense, high-quality sateen-feel cotton, and nowhere near the four-figure fantasies you see advertised. The same cloth is sold on its own as a duvet cover, fitted sheet and pillowcase pair.

Where thread count stops being the point

Our Cloud Cotton and Plain Cotton are both 200 thread count — and Cloud Cotton feels nothing like Plain Cotton. Same fibre, same density, completely different hand.

The difference is the weave. Cloud Cotton uses a double-layer construction that traps air between two fine layers, which is what gives it loft and that airy, cloud-like feel. Plain Cotton is a single-layer weave: flatter, crisper, more traditional.

This is the single most useful thing to understand about thread count: it tells you about density, not about feel. Two fabrics at the same count can sit at opposite ends of the comfort spectrum depending on how they are constructed.

GSM: the right unit for linen

Thread count is close to useless for linen, because flax yarns are thicker and more irregular than cotton by nature — a low count can mean a substantial, beautiful cloth. Linen is measured in GSM: grams per square metre, a straightforward measure of weight.

As a rough map:

• Under 150 GSM — light, summer-weight, can feel thin and wear out faster
• 160–180 GSM — the sweet spot for bedding: substantial enough to drape and last, light enough to breathe
• Over 200 GSM — heavy, slower to soften, better suited to upholstery than a duvet cover

Our linen is 170 GSM, 100% French flax, stonewashed. That sits deliberately in the middle: enough weight to hang properly over the side of a bed rather than clinging, without the density that makes cheap heavy linen feel like canvas for the first year.

Momme: the silk unit

Silk uses its own measure again. Momme (mm) is a weight unit — the weight in pounds of a piece of silk 45 inches by 100 yards. Higher momme means denser, heavier, more durable silk.

• Below 16 momme — thin. Often used for scarves and linings; too fragile for sleepwear you wash regularly
• 19 momme — the industry standard for quality silk sleepwear and pillowcases. Durable enough for repeated washing, still light. See the Black Roses long set.
• 22 momme — noticeably denser and more opaque, with better drape and a longer life. The premium tier, as on the Cream Cockatoos set.

Our silk sleepwear is 19 momme, with a 22 momme range above it. There is no 12 momme anywhere in the shop, which is where most "affordable silk" actually sits.

The cheat sheet

Fabric	Unit	Our spec
Silky Cotton	Thread count	300 TC, sateen
Cloud Cotton	Thread count + weave	200 TC, double-layer
Plain Cotton	Thread count	200 TC, single layer
Linen	GSM	170 GSM, French flax, stonewashed
Mulberry silk	Momme	19 and 22 momme

What to ask instead

If a bedding page gives you a number and nothing else, ask three questions:

1. What unit is that in? A four-figure thread count is either metric or inflated.
2. What is the weave? Density without construction tells you nothing about how it will feel.
3. What is the fibre and where is it from? Long-staple cotton at 300 beats short-staple at 800, every time.

Full specifications for every fabric we make are on the bedding fabrics page, and you can compare them side by side in the bedding builder.