The non‐self‐similar diffusion of energy from an enclosure is investigated for plane parallel geometry for the case where the transport of energy is purely radiative. The energy released instantaneously in the cavity is partitioned in arbitrary proportions between radiant energy and internal energy of matter. The mean free path of radiation in the walls bounding the enclosure varies as the cube of the temperature, but the material within the enclosure is assumed to be transparent to radiation.Solutions for the non‐self‐similar radiative diffusion of radiation from the cavity are expressed in parametric form and numerical results are displayed graphically. In addition, series solutions are given which apply in the limit of short and long times after the initial release of energy in the cavity.