An underwire bra is a brassiere that utilizes a thin, semi-circular strip of rigid material fitted inside the brassiere fabric. The wire may be made of metal, plastic, or resin.

An unlined bra, by definition, is a bra made with one layer of fabric across the cups, no padding or foam included. The benefits of unlined bras are primarily rooted in comfort.

Wireless bras give support and shape without the underwire. Wireless bras are good for all bust types. They may also be called: soft-cup bras, wire-free bras, and non-wire bras.