Sphere-pac fuel, together with Vipac fuel, is one of the most elaborate particle fuel concepts. In Chapter 00059, Sphere-pac and VIPAC, the Sphere-pac and Vipac concepts are discussed from a more general perspective, explaining the motivation, the production technique, and the application of the concepts. Several examples of conducted programs are given. The present chapter concentrates mainly on the modeling of the Sphere-pac, with some explanations about Vipac modeling too, and only a short introduction is given to both particle fuel concepts.