This paper describes a new cushion using a urethan within an air cell (UA cell). In order to reduce vibrations of occupants, we propose the UA cell enable to control mechanical properties by an air pressure in the vehicle seat. It is necessary to clear mechanical properties of UA cell for the reduction of vibration. The purpose of this paper is to clarify the mechanical properties of the UA cell when the air pressure of the UA cell changes. In this study, the UA cell consisted of a liner polyethylene and the urethan is designed. Relationships between the air pressure and the mechanical properties of UA cell are examined by a measurement using a vibration exciter. From these results, frequency response functions are changed by controlling the air pressure. A spring constant and a viscous damping coefficient are estimated from the frequency response functions. Relationships between the air pressure and mechanical properties are approximated by a 7th‐degree function. In addition, the variation range of the UA cell is wider than that of the air cell in the mechanical properties when the thickness of the UA cell and the air cell are changed within the same range. Therefore, it was shown that the UA cell could be used as an actuator to control the mechanical properties.