Abstract: A flexible membrane for a polishing head includes a main part having a first surface configured to make contact with a surface of a substrate and a second surface opposite to the first surface, a plurality of extensions extending substantially perpendicularly from the second surface of the main part so as to define a plurality of independent spaces, respectively, and an inner ring coupled with an inner side of an outermost extension of the extensions to support an edge portion of the main part. A bottom surface of the inner ring is substantially flat.