The T-shirt spent decades as underwear before anyone wore it outside

A knitted layer under a woven one

For most of the nineteenth century, an undergarment was something you were laced or buttoned into, frequently a one-piece knitted union suit covering the whole body. It was warm, it was awkward, and in hot conditions it was miserable.

The T-shirt is what you get by cutting that garment in half and simplifying what remains: a knitted cotton pullover with short sleeves, no fastenings and a round neck. Knitted rather than woven, which matters, because a knit stretches enough to be pulled over the head without buttons, and it lies against the body without needing to be fitted.

Its function was straightforward. It absorbed perspiration and body oils and could be washed hard and often, protecting the more expensive woven shirt worn over it. That is the same reason a shirt was worn under a jacket, applied one layer further in.

Navies and hot weather

Navies were early adopters, and the reasons are practical rather than stylistic. Sailors worked hard in confined spaces, often in tropical heat, and a light knitted undershirt was far more tolerable than the alternatives while remaining cheap enough to issue in quantity and simple enough to launder in bulk.

The name is generally taken from the shape: laid flat with the sleeves out, the garment forms a T. It is a description rather than a brand, which is part of why it stuck.

Work followed the same logic on land. In hot trades men stripped off the outer shirt and worked in the undershirt, which was tolerated on a factory floor or a farm and would have been unacceptable on a street. That distinction — the same garment being decent in one place and not in another — is the interesting part of the story.

The war moved it into the open

Mass mobilisation in the Second World War put a simple cotton undershirt on an enormous number of young men, and put them in situations where the outer layer came off routinely. Photographs from that period show it worn as an outer garment as a matter of course.

Servicemen came home accustomed to wearing it and kept doing so, initially for physical work and around the house rather than in public. Surplus supply helped, as it always does. A garment that is abundant and cheap gets worn.

Film in the following decade completed the transition by putting it on screen as deliberate costume, and it acquired an association with youth and with a certain rejection of formality that it has never entirely lost. The garment did not change. Its meaning did.

Printing turned it into something else again

The second transformation was technical. Screen printing on textiles made it cheap to put an image or a few words onto a plain shirt in small quantities, and that turned a garment into a surface. A T-shirt could now say something, and it could be produced in a run of fifty for an event or a cause.

This is genuinely unusual. Very few garments function as a communication medium, and none does it as cheaply. The T-shirt became the standard way to mark membership of something — a team, a workplace, an argument — and it did so without any change to its construction.

The economics reinforced it. A garment made from a single knitted cloth, with four seams and no fastenings, is about as cheap as clothing gets to manufacture, which is why it became the default carrier for print rather than any other garment.

What its construction still tells you

The T-shirt is a knit, and everything discussed elsewhere about knits applies to it. It stretches in all directions, it bags where it is repeatedly loaded, it curls at a raw edge and it pills. The neck opening is usually finished with a rib band because plain jersey would stretch out permanently within weeks.

That neckband is the single best indicator of how a T-shirt was made. A band that is dense, evenly attached and slightly narrower than the opening it is set into will hold its shape; a thin one, stretched as it was sewn, will be loose and wavy after a few washes and cannot be repaired.

It is a good illustration of a general point about clothing. The most-loaded, most-visible small component is usually where cost is cut and where the garment fails first, and on a shirt with no buttons, no lining and no pockets, that component is the collar.