Abstract: A piston is provided for use in a free-piston engine and includes a crown portion having a predetermined thickness, a plunger connection portion having a passage extending therethrough along the axis of the piston and being connected to the crown portion, a sealing portion extending from the crown portion, and a strut portion having a plurality of struts disposed between the sealing portion and the plunger connection portion. The piston of the subject invention provides a compact, high strength, low weight design that is effective in use to provide efficient operation and effectively conduct heat from the piston during use.