The carbon fiber strip is laminated to the bottom of the surfboard or SUP to increase the stiffness so it doesn't bend when standing on it.Carbon fiber provides great strength when put in tension (the force on the bottom of the board from bending) and is a substitute for the traditional wood stringer.Incorporating a carbon stringer on the bottom of a stringerless blank eliminates the wood shaping tools needed and fussing with keeping the stringer flush with the foam when shaping, reducing some of the work.Simply laminate the carbon strip right to the foam and roll the bottom layer of fiberglass right over it and continue laminating the bottom. All in one step...