A heatsink having tapered geometry that improves passive cooling efficiency is discussed. A tapered geometry between heatsink heat dissipation elements, as a function of distance along a z-axis opposing gravity, decreases resistance to rarification of passively flowing cooling gas upon heating. Thus, the tapered heatsink elements result in higher velocity of gas flow and increased cooling efficiency of the heatsink. Optionally, the heatsink is made from a thermally conductive polymer allowing the heatsink to be created in complex shapes using injection molding.