Valve for controlling pressurized air flow to an inflatable air cell in a vehicle seat, comprising: a housing enclosing a valve chamber communicating with a spigot for supplying pressurized air to the inflatable air cell and having an input opening in fluid communication with a pressurized air supply passageway, and a venting opening for venting off air to the ambient atmosphere; a moveable valve piston biased towards a valve seat formed at the input opening and configured to close the input opening when the valve piston is in abutment on the valve seat to block communication with the pressurized air supply passageway; an actuator configured to, when activated by electric energy supply, pull the valve piston away from the valve seat to open the input opening to establish fluid communication from the pressurized air supply passageway to the valve chamber and the spigot; and a venting control mechanism (20, 50) configured to close the venting opening in response to opening of the input opening by activation of the actuator and vice versa; characterized in that the venting control mechanism comprises a rolling diaphragm which envelopes a top portion of the valve piston and which separates the valve chamber from a space which is in fluid communication with the ambient atmosphere, and in that the vent opening is formed as an opening through the rolling diaphragm located such that, when the valve piston is, via a central head portion of the rolling diaphragm, in indirect abutment on the valve seat, the venting opening at least partly lies in a convolution area of the rolling diaphragm between the valve piston and a surrounding wall and is thus open to the space in fluid communication with the ambient atmosphere, whereas, when the valve piston has been pulled away from the valve seat by activation of the actuator, the convolution area has moved along the rolling diaphragm and the vent opening has moved out of the area of the rolling diaphragm in fluid communication with the ambient atmosphere. a housing enclosing a valve chamber communicating with a spigot for supplying pressurized air to the inflatable air cell and having an input opening in fluid communication with a pressurized air supply passageway, and a venting opening for venting off air to the ambient atmosphere; a moveable valve piston biased towards a valve seat formed at the input opening and configured to close the input opening when the valve piston is in abutment on the valve seat to block communication with the pressurized air supply passageway; an actuator configured to, when activated by electric energy supply, pull the valve piston away from the valve seat to open the input opening to establish fluid communication from the pressurized air supply passageway to the valve chamber and the spigot; and a venting control mechanism (20, 50) configured to close the venting opening in response to opening of the input opening by activation of the actuator and vice versa; characterized in that the venting control mechanism comprises a rolling diaphragm which envelopes a top portion of the valve piston and which separates the valve chamber from a space which is in fluid communication with the ambient atmosphere, and in that the vent opening is formed as an opening through the rolling diaphragm located such that, when the valve piston is, via a central head portion of the rolling diaphragm, in indirect abutment on the valve seat, the venting opening at least partly lies in a convolution area of the rolling diaphragm between the valve piston and a surrounding wall and is thus open to the space in fluid communication with the ambient atmosphere, whereas, when the valve piston has been pulled away from the valve seat by activation of the actuator, the convolution area has moved along the rolling diaphragm and the vent opening has moved out of the area of the rolling diaphragm in fluid communication with the ambient atmosphere.