A system includes a power source and a heat-shield mechanism which encloses the power source. This heat-shield mechanism includes a 3-dimensional housing that defines a cavity in which the power source resides, and a plate that is positioned to cover an opening to the cavity that is defined by an edge of the housing. Note that the housing contains three layers in which a second layer is sandwiched between a first layer and a third layer. This second layer has a first anisotropic thermal conductivity. Furthermore, the plate includes a material having a second anisotropic thermal conductivity.