Underwire is a type of support used in bras, typically made from metal or plastic. It is sewn into the fabric beneath the cups to help lift and shape the breasts, providing a more defined silhouette. The underwire follows the natural curve of the breast and is designed to enhance comfort and fit. Many women choose bras with underwire for added support, especially in larger cup sizes. However, some may find underwire uncomfortable or restrictive. Alternatives like wireless bras or bralettes are available for those who prefer a softer fit while still offering support.