underwire

An underwire is a semi-rigid arc, usually made of metal or plastic, that is sewn into the cup or a channel along the bottom edge of a bra to provide lift, support, and shape. The wire is typically encased in fabric and ends are capped to prevent poking. Underwires can be made from steel, aluminum, or flexible plastic, and many are coated or wrapped to reduce skin irritation. Some designs use flexible or “soft” wires that bend with movement, while others apply a stiffer wire for stronger support.

Purpose and function. The underwire helps maintain the cup’s shape, positions the breast forward, and can improve projection and separation. It is most common in everyday, semi-sheer, and molded-cup styles, as well as many push-up and balconette designs. Underwires are less common in certain bralette or wireless styles, which rely on fabric and elasticity for support.

Construction and varieties. Wires are usually placed along the lower interior of the cup and sometimes along the side edge, forming a U- or C-shape that follows the breast’s base. Some bras use a stitched channel for a fixed wire, while others insert the wire into a sewn sleeve to allow replacement or cleaning. Materials vary by brand and purpose, with nickel-free options available to reduce irritation.

Care and considerations. Proper fit is essential to comfort; an ill-fitting underwire can cause poking, skin irritation, or breast tissue discomfort. Wires can bend or break if the bra is damaged or worn out, so checks for wear are advised. When in doubt, a well-fitted wireless or soft-cup design can be an alternative.

Contemporary use. Underwires remain common in many bras worldwide, though there is growing availability of wireless and lightly structured options for those who prefer not to wear a structured underwire.