A hair roller for wrapping therearound a hair portion is a concave cylinder, which has a normally oval cross section at a top portion and a bottom portion thereof larger than a normally oval cross section at a middle portion thereof of an oval cylinder; an oval cylinder, which has at least one normally oval cross-section, or a concave oval cylinder. The hair roller is optionally provided with a hair-retaining structure formed on the roller body for grabbing the hair portion.
1. A hair roller, comprising a roller body for wrapping therearound a hair portion, wherein the roller body is a continuously curved concave cylinder, which has a normally oval cross section at a top end and a bottom end thereof larger than a normally oval cross section at the midpoint thereof, wherein none of the cross sections from the top end to the midpoint have the same area; and none of the cross sections from the bottom end to the midpoint have the same area.
2. The hair roller according to claim 1 , further comprising a hair-retaining structure formed on the roller body for grabbing the hair portion and/or confining a movement range of the hair portion on the roller body.
3. The hair roller according to claim 2 , wherein the hair-retaining structure includes bristles, a piece of hooks and/or loops attached onto the roller body, grooves provided on the roller body for receiving therein the hair portion, or a combination thereof.
4. The hair roller according to claim 1 , wherein the roller body is a hollow cylinder.
5. The hair roller according to claim 4 , further comprising a cushion material and/or a heat-conductive material formed inside the hollow cylinder.
6. The hair roller according to claim 1 , wherein the roller body is a solid oval cylinder.
7. The hair roller according to claim 6 , further comprising a plurality of channels distributed in the solid oval cylinder for inserting or filling therein a heater material, which can spontaneously dissipate heat and/or be heated after being placed in the channels.