A heat pack includes a housing, a first phase change material (PCM) that is contained in the housing, and a thermal storage buffer that is contained in the housing. The thermal storage buffer includes a second PCM. An initiator is in operative contact with the first PCM. Activation of the initiator causes crystallization of the first PCM, and the first PCM cooperates with the thermal storage buffer to provide heat at a predetermined temperature range upon crystallization of the first PCM.

A fertility-enhancing cooling seat for lowering temperatures of human testicles so as to increase sperm quality and quantity. The cooling seat includes: a top flexible portion and a base portion; a bottom flexible portion coupled to the top flexible portion, the bottom flexible portion forming a seal with the base portion, portions of the bottom flexible portion and portions of the top flexible portion defining isolated cooling cells with cooling-cell volumetric spaces; a phase-change material located in the cooling-cell volumetric spaces, the phase-change material configured to change from a solid phase to a liquid phase at a first temperature and that is configured to change from a liquid phase to a solid phase at a second temperature that is lower than the first temperature. At least one of the isolated cooling cells defines a diameter that is larger than a diameter of the other of the cooling cells.