Plastic underwire for underwear is a supportive structure used in the construction of bras and other types of underwear. This type of underwire is made from a flexible plastic material that is often encased in fabric to provide comfort and prevent irritation. Plastic underwire is a popular alternative to metal underwire due to its lightweight design, flexibility, and resistance to rusting or tarnishing. It allows for a better fit, lift, and shaping, providing the wearer with the necessary support and comfort.