This is that strip of wood you see running down the middle of your surfboard. It provides strength and a center for “flex” in your board. Often times the stringer is made out of balsa wood, but other stronger woods and materials may be used as substitution.
Some boards, usually for bigger waves, are equipped with more than one stringer for extra strength.
New, alternative surfboards like Surftech, Salomon and Aviso do not have wooden stringers and rely, rather, on the strength and flex of the materials they’re built with.
Other stringer designs are being used as well, for example, the parabolic stringer does not feature a stringer running down the center of the board, but rather two on the rails to create a unique liveliness and flex for an unparalleled surfing experience.