Abstract: The element with variable shape (1) is composed of a cushion (10), having inside a fixed frame (20), which involves a lower section (13) of said cushion (10) and two symmetrical movable frames (25A), (25B), hinged above said fixed frame (20) and aimed at involving an upper section (14) of the cushion (10). The movable frames (25A), (25B) can rotate by 180° independently from each other, to direct a respective portion (14A), (14B) of said upper section (14) from an external horizontal configuration (HE) to an inner horizontal configuration (HI), passing through a vertical neutral configuration (N), in which the portion (14A), (14B) is substantially aligned with said lower section (13). The back (100) and sides (110) of a sofa (D) or armchair (P) are defined by respective elements (1), which can be configured in many ways so as to offer the maximum sitting comfort.