Discussions are made among the polyhedral superconductors made from IVth-group elements (C, Si and Ge). Important superconducting physical parameters of Ba 8 Si 46 are deduced from magnetic measurements and are compared to those of K 3 C 60 . Using the lower and the upper critical fields of 78 and 5:5 Â 10 4 Oe determined by magnetization measurements, the penetration depth l ¼ 270 nm and the coherence length x ¼ 7:7 nm are estimated for Ba 8 Si 46 . The high density of states at the Fermi level is the most important parameter to give rise to a relatively high T c in Ba 8 Si 46 , while the high phonon frequency is essential for K 3 C 60 . In contrast, the experimental facts found in IV 100 where IV ¼ Si and Ge imply that the rattling phonons in the open cage potentials seem to control the superconducting transition temperature. r