Fuel capsules usable in inertial confinement fusion (ICF) reactors have shells made from materials having a diamond (sp3) lattice structure, including diamond materials in synthetic crystalline, polycrystalline (ordered or disordered), nanocrystalline and amorphous forms. The interior of the shell is filled with a fusion fuel mixture, including any combination of deuterium and/or tritium and/or helium-3 and/or other fusible isotopes.