where P is the input power, r is the radius of the sensor, λ is the thermal conductivity, and D(τ) is the shape function, 2 recorded during the TPS measurement (Figure S-1). The samples were pressed into pellets using a Carver press inside an Argon glove-box. The pellets were pressed using a pressure of 70-100 MPa until a free-standing pellet is formed. The packing density of the pellets was determined by measuring the mass and the thickness of the pressed pellets. A Hot Disk Sensor was used which consists of an electrically conducting pattern fitted between the metal hydride pellets. The sensor applies an electrical current, high enough to increase the temperature of the samples up to several degrees (typically between 2 and 4 K). At the same time, the sensor records the resistance (temperature) increase as a function of time. The heat generated dissipates through the sample on either side at a rate dependent on the thermal transport characteristics of the material.