Why Do Bras Have Underwires? The What, When, How, and Why

As far as bra components go, underwires are probably the most infamous. They snap and shift and shank us at the least convenient moments, and many of us have given up underwire bras altogether to opt for something less structured. 

This leads us to two questions: What is the actual purpose of underwires in bras? And secondly, is it possible to find an underwire bra that is comfortable? 

Keep reading to discover the why and how of underwires in bras!

The What: What Exactly is an Underwire?

Underwires are rigid semicircles sewn into the band of a bra, at the front and just under the breasts. The underwires are made from materials like plastic, metal, or resin; most bras use a steel underwire. 

Underwires range in shapes because they are designed to follow the curve of one’s breast root (where the breast joins the body). They are offered in three categories of shapes, and depending on your needs you’ll benefit from different underwire shapes:

J-Shaped Underwires

J-shaped underwires are found in everyday bras, from balconettes to demi bras. These underwires are suited for a variety of breast root shapes, and the lower center can accommodate close-set or touching breasts. If you are unfamiliar with all of these bra style terms, head over to our Encyclopedia of Bras to learn more! 

J-shaped underwires illustration

Plunge/Rocker Underwires

Plunge/rocker wires are banana-shaped wires that can accommodate wide breast roots that do not require much support. Meanwhile, a shorter wire means that they can be more comfortable for women with short torsos or high-set breasts. They are typically used in plunge and push-up bras. 

plunge underwires illustration

U-Shaped Underwires

The third style is a U-shaped underwire. With longer wires, they are often used in strapless bras (not reliant on a shoulder strap for support) and in bras designed for larger breasts, such as larger than a cup size D. U-shaped wires can give a centering effect and are generally suitable for women with narrow breast roots, because they do not stretch as wide as plunge or J-shaped underwires.

U-shaped underwires illustration

The When: The Birth of Underwires

Back in 1893, an American woman named Marie Tucek received a patent for a “breast supporter”. Like a modern bra, her invention featured two cups for breasts and hook-and-eye fasteners in the back. 

patent for bra 1893

Notably, the patent also included the incorporation of cardboard or metal (or another stiff material) to lift the bust from underneath – as an underwire does in modern bras.

In the 1930s, another American inventor named Helen Pons patented a bra with an “open-ended wire loop” that was similar to U-shaped underwires in bras today. The patent laid the groundwork for further underwire bras, which emerged in the following decades.

In the 1940s, businessman and movie producer Howard Hughes (portrayed by Leonardo DiCaprio in 2004’s The Aviator) commissioned an underwire bra worn by Jane Russell in one of his films. The support offered from the underwires created a more lifted, centered, and exposed bust (read: cleavage). The look gained popularity, and by the 1950s, the incorporation of underwire had become standard for everyday bras.

Today, between 60% – 70% of bras sold globally are underwire bras.

The How: How Do Underwires Work?

When studying the design of underwire bras, we were surprised to learn that the physics of an underwire is similar to the physics used in cable bridges! 

Both objects use a cantilever system to provide support and stability through the redistribution of downward tension. In a bridge, the downward force of traffic is transferred up the bridge cables, into the towers, and down into the earth. Similarly, in a bra, the weight of your breasts is transferred into the cups, up along the wires, and down to your band. For this reason, a longer wire tends to mean greater support in a bra, and a snug, stable band is particularly important for stability. (Imagine what would happen if bridge wasn’t well-anchored into the earth). 

The Why: What’s the Point of Underwires?

Many women enjoy the structure that underwire bras offer. Compared their non-wired counterparts, underwired bras offer greater definition, lift, and weight distribution.

The curved shape of underwires guide breasts into natural contours so they appear uniform and even. They also can separate the breasts, so as to avoid a “uniboob” effect. 

Underwire bras also lift breasts above their natural position. To the extent that you appreciate a heightened and lifted bustline, a properly-fitted underwire bra can help to achieve that silhouette. 

The third benefit of underwires is that they distribute the weight of your breasts close to your chest and across your torso, so your shoulders and back don’t become strained.

Do you prefer underwire or soft-cup bras? Let us know in the comments below!

To learn more about bra history, bra styles, or bra care, check out our other blog articles!

To find your perfect bra fit, head over to our Fit Quiz!

One thought on “Why Do Bras Have Underwires? The What, When, How, and Why

  1. I’m an engineer. It surprises me what people who don’t understand physics believe. Most of what I read about bra wires is simply wrong. It may be because marketing people make claims they think will appeal to customers, and customers imagine (or hope) that the claims are true. Wires do not provide lift, lift comes from the cup being pulled upwards by the strap, or from the shape of the cup pulling the breast toward the body by the band in the case of sports bras and strapless bras. The wire alters the shape of the breast root a little (but not much). Rather than looking for a bra with wire, it is better to not wear a bra at all if you can (and wear natural fabrics to avoid chaffing the breast), or wear a bra that is the right fit with the right cup size and spacing.

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