DU 701: T-Shirts Explained — From Underwear to Icon

By Eric Steffen
Founder / Maker
FITTED Underground

Most people own a dozen t-shirts and have never thought carefully about a single one. They fold them, stack them, grab whichever is on top, and move on with their day. The t-shirt is so ubiquitous, so fundamental to the daily wardrobe, that it has become almost invisible — the garment we reach for without thinking, precisely because we've never been given a reason to think about it.

This article changes that.

By the end of it you'll understand what goes into a great t-shirt — the history, the construction, the cotton, the weight — and why the difference between a mass produced tee and a high quality tee is not a markup. It's a material reality.

Before the T-Shirt — Two Thousand Years of Undershirts

The t-shirt didn't arrive from nowhere. It is the direct descendant of a garment humans have worn for at least two thousand years, performing the same function it always has.

In ancient Rome, men wore a garment called a "subucula" beneath their tunics — a simple linen undershirt whose job was exactly what you'd expect: absorb perspiration, protect the outer garment, provide a removable layer for warmth. The function was fully formed 2,000 years ago. Medieval Europe had the "chemise" — linen, worn next to the skin by both men and women, the hygiene layer between body and clothing. Outer garments were expensive and rarely washed. The chemise was changed and laundered regularly. The quality of your chemise — the fineness of the linen, the embroidery at the cuffs — was a subtle signal of social status, sometimes deliberately allowed to peek out at the sleeve. Sound familiar?

The core logic of the undershirt has never changed: keep perspiration away from your outer clothing, provide a layer you can remove if you get warm, and protect the more expensive garment from the inevitable reality of wearing it against a human body. That's it. That's the entire brief. The t-shirt we know today is simply the most refined, most democratic expression of a solution that has been working for two millennia.

What changed in the twentieth century was not the function. It was status.

From Underwear to Icon — The American T-Shirt

Around 1913, the US Navy began issuing a collarless cotton undershirt as standard uniform issue, worn beneath the outer uniform. The Army followed in World War I. By the end of World War II, millions of American men had worn one daily, for years, in every climate imaginable. When they came home, some kept wearing them — not as underwear, but as clothing. The undershirt had begun the jump from underwear to outerwear.

Two films finished the job.

In 1951, Marlon Brando played Stanley Kowalski in A Streetcar Named Desire in a white t-shirt — something that had previously been hidden now worn as the entire statement. Raw physical presence. The garment stripped of everything but itself. Two years later, James Dean wore one in Rebel Without a Cause. The white tee as youth, defiance, the refusal to dress up for a world that hadn't made room for you yet. To complete the outfit, he wore blue jeans beneath it. There it was, the complete uniform that would define American casual dress for the next seventy years. These weren't costume choices. They were cultural declarations. The undershirt had become outerwear, and it was never going back. The blue jean was a cultural statement of a country grounded in hard work and a new world order. The American century was here. 

What followed was a golden age. Paul Newman wearing his t-shirt and jeans with the ease of a man born into it. Steve McQueen making it look like the most intentional choice in the room. The Fonz — leather jacket, white tee underneath, and somehow the tee did half the work. Grease (1978) — the white t-shirt as the uniform of American working-class cool, worn by people who couldn't afford to care about fashion and ended up defining it anyway.

American t-shirt manufacturing at its peak produced garments built to last — ring-spun cotton, careful construction, fabric that softened and improved with washing rather than thinning and pilling. Then the same story as denim: offshore production in the 1980s and 1990s, cheaper cotton, faster machines, thinner fabric. By the 1990s the mass-market tee had become a commodity. Competent. Disposable. Designed to be replaced rather than worn out.

The difference between a great t-shirt and a forgettable one starts with understanding what actually separates them. That starts with how the fabric is made.

Knit vs. Woven — Why a T-Shirt Isn't Made Like Denim

Denim is a woven fabric. It's made on a loom — warp threads running lengthwise, weft threads running across — producing a flat sheet of cloth. The selvedge are the self-finished edges of that flat sheet. It gets laid flat, cut and then sewn.

T-shirt fabric is different at the most fundamental level. It's knitted, not woven — and it's produced as a tube, not a sheet. A circular knitting machine holds hundreds of needles arranged in a cylinder. A single continuous yarn loops around and around those needles, building up the fabric as it goes — layer by layer, round by round. The result is a seamless tube of jersey knit fabric that stretches, drapes, and behaves completely differently from woven cloth. Cut edges don't fray the same way. The fabric has stretch in every direction. It recovers its shape after being pulled.

All t-shirt fabric starts as this tube. What happens next is where the first construction decision gets made.

A tubular t-shirt uses the tube as-is — the tube becomes the body of the shirt, with no side seams at all. It can be fasterer to produce, and the garment has no sideseams giving a luxurious feel. The trade-off: because the knit structure has a natural directional torque, tubular tees tend to twist after washing.

A side-seamed t-shirt cuts the tube into panels — front and back — and sews them together along the sides. The extra step can add construction time but it does allow for a more precise fit because the panels can be shaped to follow the body rather than being constrained by the tube's circumference.

Both have tubular and side seamed t-shirts have their benefits and draw backs. But that's not the only — or even the primary — signifier of a quality tee.

The Cotton — From Basic to Exceptional

The knitting method matters. The construction matters. But cotton is where a t-shirt is ultimately won or lost — and the spectrum runs from mass-market commodity to genuinely extraordinary.

Open-end spun (carded) cotton is the baseline. A fast, efficient spinning method that produces a slightly rougher, less consistent yarn. The cotton in most mass-market tees. Gets the job done.

Ring-spun cotton is the significant upgrade. The yarn is twisted and thinned more carefully during spinning, producing a smoother, stronger, more consistent thread. Noticeably softer in the hand. The standard for any t-shirt worth paying attention to.

Combed and ring-spun cotton adds an extra step before spinning: short fibers and impurities are combed out, leaving only the longest, cleanest fibers. The result is smoother, more uniform, and softer still.

Japanese ring-spun cotton is not a different variety of cotton — it's a different spinning philosophy. The same craft attention that Japanese mills apply to selvedge denim yarn, applied here to jersey knit cotton. The result is a ring-spun cotton with a distinctive softness that develops further with washing and wear. The more you wash it, the better it gets.

Supima cotton is grown exclusively in the American Southwest from Gossypium barbadense — a long-staple variety that produces fibers significantly longer than standard cotton. Longer fibers mean stronger, finer, smoother yarn. The fabric is softer, more lustrous, and holds its shape and color longer than standard cotton. "Supima" is a trademarked designation — it means the cotton was grown in America and certified to standard. One of the two finest cottons in the world.

Giza cotton (the specific designation within Egyptian cotton) is also Gossypium barbadense, grown in the Nile Delta. Extra-long staple, extraordinarily soft, produced in smaller quantities. "Egyptian cotton" is one of the most widely misused labels in the textile industry — "Giza" is the specific term worth looking for when you want the real thing.

Weight — GSM vs. Ounces, and Why Neither Wins

T-shirt weight is measured in two systems depending on where the fabric is made. GSM — grams per square meter — is the global mill standard used by most manufacturers. Ounces per square yard is the traditional American standard still used by many domestic brands. They're measuring the same thing: how much cotton is in a given area of fabric.

To convert, divide the GSM figure by 33.9 to get the approximate ounce equivalent. The chart below gives the common reference points, rounded to the nearest 5gsm:

Oz / sq yd	Approx. GSM*
Lightweight 4 oz	135 gsm
5 oz	170 gsm
Midweight 6 oz	205 gsm
7 oz	240 gsm
Heavyweight 8 oz	270 gsm
9 oz	305 gsm
10 oz	340 gsm
11 oz	375 gsm

*GSM figures rounded to the nearest 5gsm. Exact conversions vary slightly by mill.

What the weight actually means in wear is simpler than the numbers suggest.

Lightweight (130–165gsm / 4–5oz) drapes beautifully, breathes well in warm weather, and has an almost translucent quality in white. This is your summer tee — not a compromise, but a deliberate choice for a specific condition.

Mid-weight (205–240gsm / 6-7oz) is the year-round standard. Substantial enough to hold its shape and opaque enough to wear confidently, light enough to wear comfortably across seasons. The most versatile weight in the range.

Heavyweight (270gsm+ / 8oz+) is built for cooler months — and for people who want their t-shirt to function almost like a woven shirt. A 305gsm tee is meaningfully wrinkle-resistant. It holds its structure through a long day. It can go to dinner without looking like it came from a gym bag. The weight that surprises people most, in the best way.

One weight is not better than another. They serve different purposes. The right answer, honestly, is all three.

The Perfect Fitting T-Shirt — FITTED Underground's PFT

When we set out to make our tee, we had a very specific goal — and a very specific name for it. The original name was, well ... the Perfect F*cking T-Shirt. Hey, we're from Brooklyn. What do you expect!? That was exactly what we were trying to make, and there was no more honest way to say it. We've cleaned it up to the Perfect Fitting T-Shirt for the sake of decorum — a little less Brooklyn, but it still works.

Here's how we built it:

1. Fit: We started where we always start: the cut. Not too long at the waist. Not too long at the sleeve. Definitely no super-wide sleeve opening that makes any arm look formless. Side-seamed for shape retention. Shoulder seam placed exactly where it belongs. A collar that holds its shape after a hundred washes. 
2. Fabric: We knew not just any fabric would do, so we searched for the best — and we found them. We make three PFTs, each a different expression of the same idea.
   1. The PFT 185 is 185gsm Supima cotton — our lightweight option. American Supima grown in the Southwest, milled, cut, and sewn in the United States. An end-to-end American lifecycle you won't find many other places in this country. The summer tee that doesn't feel like a compromise.
   2. The PFT 220 is 220gsm Japanese ring-spun cotton — our mid-weight option. The fabric draws from the same Japanese craft tradition that produces the world's finest selvedge denim: ring-spun with care, attentive to yarn consistency and surface quality, with a softness that develops further with each wash. The more you wear it, the better it gets.
   3. The PFT 305 is 305gsm Supima cotton — our heavyweight option. Wrinkle-resistant, structured, the tee you wear when you want to look like you thought about it. Still Supima. Still American end to end. Put it on and you'll understand immediately why we call it the heavyweight — it has the presence of something more than a t-shirt.
3. Finish: The fit on day one had to be the same as the fit after a hundred wears — which meant pre-washing every tee before it leaves the workshop, removing shrinkage and softening the fabric so there are no surprises.

We feel like we're spoiling ourselves every time we put one on. We are. But we deserve it every once in a while — and so do you.

The PFT is part of the same value tradition as everything else we make. Buy quality. Enjoy quality. Buy fewer, better things. A great t-shirt worn for five years costs less per wear than a cheap one replaced twice a year — and it feels better every single time you put it on. That's not a luxury argument. That's arithmetic.

What Comes Next

The t-shirt is the foundation of the American casual wardrobe. The next garment in the 700-level is one that's been quietly essential to that wardrobe for over a century — work pants that became street wear, military surplus that became style. That's DU 702: Fatigue Pants Explained.

← Previous: DU 106 — Denim Dictionary  |  Next: DU 702 — Fatigue Pants Explained →

Further Reading

• A Brief History of the T-Shirt — Smithsonian Magazine
• How Loopwheel Fabric Is Made in Wakayama, Japan — Permanent Style
• About Supima Cotton — Supima
• How to Recognize Loopwheeled Products — Heddels

Eric Steffen is the founder of FITTED Underground, a custom jeans and raw denim workshop at 108 Bayard Street in Williamsburg, Brooklyn. He has been making jeans by hand since 2014. Denim University is his attempt to share everything he's learned — about the history, the craft, and the culture behind the world's most enduring garment.