Abstract: A regenerator for a magnetic heat exchanger is provided. The regenerator comprises a housing having a chamber, an inlet and outlet for a working medium, and a chamber volume V. At least one magnetocalorically active component is arranged in the chamber between the inlet and the outlet and has at least one inner flow channel with a hydraulic diameter dhyd. The volume of the chamber not occupied by the magnetocalorically active component provides at least one bypass flow channel, both the inlet and the outlet being reached from the at least one bypass flow channel, and this bypass flow channel having a hydraulic diameter D, where D>dhyd. The at least one inner flow channel of the magnetocalorically active component is in flow communication with the bypass flow channel. The magnetocalorically active component and the at least one bypass flow channel are arranged parallel to one another.