Zigzag spring (also called sinuous spring, no-sag spring, or serpentine spring) is a type of spring commonly used in furniture, particularly sofas, chairs, and mattresses, to provide flexible and durable support.

• Shape: Made from a continuous steel wire bent into a repeating "S" or "M" pattern. Resembles a zigzag or wavy line, hence the name.
• Material: Typically made from high-carbon steel or tempered steel for durability. May be coated with zinc, vinyl, or epoxy to prevent rust and reduce noise.
• Function: Provides flexible yet firm support for seating surfaces. Absorbs weight and returns to shape, preventing sagging over time. Often used in place of traditional coil springs for cost efficiency and ease of installation.