Super 100s to 150s: What Super Numbers Mean on Suit Fabric

Super 120s is one of the most common labels you will see on a good suit, and one of the most misunderstood. The number is often presented as a quality score, with the suggestion that Super 150s must be better than Super 120s. It is not a quality score. It measures how fine the wool fibers are, under an international code and, in the US, under federal law. Once you know what it measures, you can read a fabric book with confidence and avoid paying extra for a fabric that will wear out sooner.

What does Super 120s mean?

Super 120s means the wool in the fabric has a mean fiber diameter of no more than 17.75 microns. A micron is one thousandth of a millimeter, so these fibers are several times finer than a typical human hair. The figure is an average: every fleece contains a spread of fiber diameters, and the label refers to the mean of a measured sample. Two fabrics labeled Super 120s can therefore differ slightly in real fineness, as long as both sit at or under the limit.

The same logic runs through the whole scale. Super 100s means 18.75 microns or finer, Super 150s means 16.25 microns or finer, and each step of 10 in the Super number takes half a micron off the limit. The finer the fiber, the more fibers it takes to make a yarn of the same thickness, which is why fine fabrics feel softer and drape more fluidly.

Super number to micron chart

This is the full scale from the code of practice of the International Wool Textile Organisation (IWTO). The figures are maximums: a Super 120s fabric may be finer than 17.75 microns, but not coarser.

Where do Super numbers come from?

The numbers began as a spinning measure. Under the Bradford count system used in the English wool trade, a wool's number was the count of hanks of yarn, each 560 yards (512 m) long, that a spinner could make from one pound (454 g) of combed wool. Finer wool could be spun into more hanks, so a 60s wool was finer than a 50s wool.

Over time the numbers became a selling point, and a selling point needs a measurable definition. The IWTO code provides one by tying each Super number to a maximum mean fiber diameter measured in a laboratory. In the US, the Wool Suit Fabric Labeling Fairness and International Standards Conforming Act, signed in December 2006, wrote the same limits into the Wool Products Labeling Act for wool products made from January 1, 2007. Mislabeling a Super number there is a matter for the Federal Trade Commission.

The measurement itself is a laboratory test of mean fiber diameter, not a judgment by touch, so a Super label is a claim that can be checked. What it cannot check is anything that happens after the fiber is measured: how the yarn is spun, how the fabric is woven and how the suit is made.

Which fabrics can be called Super?

Under the IWTO code, the word Super applies to pure new wool, which may be blended only with rare fibers such as cashmere, mohair or silk. New wool means wool that has not been recycled from used fabric. A fabric that mixes wool with polyester, viscose or another common fiber cannot be called Super, however fine its wool.

Is Super 150s better than Super 120s?

No. Super 150s is finer than Super 120s, not better. The finer fabric feels softer, has more luster and drapes more fluidly. It also creases more readily, shows wear sooner at the seat, elbows and inner thighs, and is harder for a tailor to press and shape. For a suit you wear once a week or less, those trade-offs can be worth it. For a suit you wear three days a week, Super 120s will look better for longer.

Do higher Super numbers wrinkle more?

Yes, as a rule. Finer fibers have less bulk and spring to pull a fabric straight, so a Super 170s suit creases faster, and holds the creases longer, than a Super 110s suit of the same weight and weave. Lighter weights make it worse, and very fine fabrics are usually woven light.

Twist and weave can offset fineness. A high-twist Super 120s in an open plain weave resists creasing better than a soft, low-twist Super 100s. That is why travel and hot-weather fabrics are sold on twist and weave first and Super number second; see the best suit fabric for hot weather for examples.

Super numbers measure fineness, not quality

A Super number tells you one thing about the raw fiber. It says nothing about these factors, which matter as much for how a suit looks and wears:

• Twist. Tightly twisted yarns are stronger, crisper and more crease-resistant.
• Ply. Two-ply (two-fold) yarns, made by twisting two single yarns together, are stronger and more even than single yarns.
• Weave and density. A closely woven twill wears better than a loose plain weave of the same fiber.
• Weight. Heavier fabrics drape and resist creasing better. Our guide to year-round suit fabric sets out the weight bands.
• Fiber length and evenness. Longer, more uniform fibers make smoother, stronger yarn, and the label does not state them.
• Finishing. How the mill washes, presses and sets the fabric changes its hand and luster.

Do Super numbers matter for flannel, tweed and summer fabrics?

Less than you might expect. Woolen flannels and tweeds are often made from wool coarser than any Super grade, and deliberately so: coarser fibers give tweed its toughness and texture, and help a woolen flannel hold its brushed surface. Worsted flannels sometimes carry a Super number, usually in the everyday range.

Hot-weather fabrics follow similar logic. High-twist and open-weave summer wools tend to use moderate grades, because their job is to stay crisp and hold the fabric off your skin, and very fine fibers would work against that. The highest Super numbers appear mainly in smooth, light worsteds for dress suits, where softness and luster are the whole point.

What Super number is best for a suit?

For most people, Super 100s to 130s. Match the number to how often you will wear the suit and how hard you will use it.

Why do higher Super numbers cost more?

Ultrafine wool is scarce. Only a small share of the merino clip is fine enough for Super 150s and above, and spinning and weaving such fine fiber is slower and needs more care. You pay for that rarity. You do not get more durability for the money; you get softness and luster.

If your budget is limited, spend it on construction and fit before fineness. A well-made half canvas suit in Super 110s will outlast a fused suit in Super 150s; our guide to fused vs canvas construction explains why.

How to read a Super number on a label

Fabric books and garment labels state Super numbers in a few ways. Here is what each tells you.

How to make a fine-wool suit last

If you do choose Super 140s or above, the way you wear and store the suit decides how long it looks good. These habits matter for any wool suit, and they matter most for fine ones.

The tailor's view

Experienced cutters tend to be wary of very high Super numbers. Fine fabrics are slippery to cut, mark easily under the iron and give less help in holding the shape built into a jacket. A good tailor will usually steer a first-time customer toward Super 110s to 130s and suggest saving the finest fabrics for a second or third suit, once the customer knows how often they wear each one.

Super numbers are one line in a longer description of a fabric. Read them alongside weight, twist and weave, and choose by how you will wear the suit. For the bigger picture, see suit fabrics explained, or learn how combed and carded yarns differ in worsted vs woolen wool.

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