underwires

Underwires are curved pieces of rigid material, typically metal or hard plastic, embedded in the lower edge of many brassieres to provide lift and shape. They are designed to help support the breast tissue by distributing some of the weight away from the chest wall.

The wire is usually enclosed in a fabric channel within the cup to prevent direct contact with the skin, and runs from the center front toward the underarm area. Ends are often capped or padded to reduce irritation where the wire meets the fabric. The overall construction may also influence how the wire interacts with movement and body shape.

Materials commonly used for underwires include steel and plastic cores. Steel wires may be coated to resist corrosion and minimize skin irritation; plastic or resin wires can offer flexibility. Some modern designs use flexible or segmented wires or “soft” or “flex-wires” marketed as more forgiving, while others rely on non-wired or wireless constructions for comfort.

Functionally, underwires aim to provide support, lift, and a defined silhouette, which can be especially beneficial for larger cup sizes. However, they can cause discomfort if the bra is poorly sized or if the wire bends, pokes, or digs into the skin. Allergies to metal components and irritation from friction are possible. Regular inspection and proper care—washing according to instructions and replacing bras showing wear—help maintain safe use.

Historically, the modern underwire bra emerged in the early 20th century and became widespread in Western fashion by the mid-20th century, with variations across regions.