Abstract: A disk spring also known as a Belleville spring is used for applications where stiffness of the spring is an essential requirement and where the usual disk springs made of metal cannot be used or are impractical to use. The disk spring of the invention consists of a body having the shape of a conical shell of elastically deformable material, such as plastic resin, and reinforcing elements within the shell to establish directed resistance to specific deformations occurring in the disk spring when axially loaded.In preferred embodiments of the invention, the reinforcing elements have the shape of bodies of rotation designed and positioned within the shell in configurations chosen to satisfy specific requirements of particular practical applications. The stiffness, the spring constant and the load carrying capacity which can be achieved are considerably higher than are obtainable with customary glass fiber reinforced plastic disk springs.