Heat switches for ADRs

•Review of gas-gap heat switches used for ADRs.•Review of superconducting heat switches used for ADRs.•Presents some new data on heat switch performance vs. helium fill.•Brief review of mechanical heat switches and other concepts. Heat switches are key elements in the cyclic operation of Adiabatic Demagnetization Refrigerators (ADRs). Several of the types of heat switches that have been used for ADRs are described in this paper. Key elements in selection and design of these switches include not only ON/OFF switching ratio, but also method of actuation, size, weight, and structural soundness. Some of the trade-off are detailed in this paper.