A plunger lift for a hydrocarbon well includes a piston that is dropped into the well and then moved upwardly to lift liquid to the surface from adjacent a hydrocarbon formation. The piston includes a series of pads biased outwardly into engagement with an inside wall of the production string thereby providing an improved seal between the piston and the production string. The pads are biased outwardly by pressure from below or a pressure differential that is moving the piston upwardly. The force moving the pads outwardly are greater during upward movement of the piston than during downward movement. The piston includes a central one-piece mandrel having an upper end higher than any component of the piston and a lower end lower than any component of the piston so that impact forces are applied directly to the mandrel and not through a threaded component.