A housing contains an internal volume. A heat-sensitive device is contained by the housing and consumes a device percentage of the internal volume. The device percentage equals the percentage of the internal volume of the housing consumed by the heat-sensitive device. A phase-change material is positioned within the housing to conduct heat from the heat-sensitive device. The phase-change material consumes a percentage of the internal volume equal to 100 percent minus the device percentage minus an expansion percentage. The phase-change material expands in volume by an amount more than 75 percent of the expansion percentage upon occurrence of a phase-change event.