Abstract: A flat curler is designed for curling or undulating hair. The flat curler comprises a round bar having a bigger diameter at its ends than in its center part and an elastic band is connected to its one end to serve as a hair fixture means. A cylindrical sleeve is fitted to be longitudinally displaceable on the round bar from one end to the other. This sleeve has a longitudinal slot which is open-ended at the advance end of the sleeve. The longitudinal slot is substantially straight and axis parallel over at least the major part of the length of the sleeve. Further the longitudinal slot is closed over its total length by an overlapping edge portion that is directed opposite to the direction of the wound hair.