Sail battens are long, thin, flexible strips—typically made of fiberglass, carbon fiber, or plastic—inserted into pockets on a sailboat's sail (usually the mainsail) to support the roach, maintain sail shape, and prevent flapping. They extend the sail’s leech aft to improve aerodynamics, with types ranging from partial to full-length.

Key Aspects of Sail Battens:
Purpose: Battens provide structural support to the roach (the curved part of the sail extending past the leech), improving sail longevity by reducing flogging.

Types:
Full-Length Battens: Run from the leech to the luff (mast), providing superior shape and easier handling when dropping the sail.

Partial/Short Battens: Extend only a few feet in from the leech.

Shape Control: Stiffer, high-tension battens flatten the sail for strong winds, while softer, less-tensioned battens allow a fuller shape for lighter air.

Materials: Modern battens are usually durable fiberglass or high-performance carbon fiber.

Components: Often used with batten receptacles (pockets) that allow for adjustment and tensioning.

Battens allow for a more aerodynamic "airfoil" shape and are essential for controlling the draft in a sail.