A numerical model is demonstrated for the pyrolysis of a spherical thermoplastic sample in microgravity including effects of bubbles. The model combines nucleation, growth, and migration of individual bubbles in 3-D space with a finite element model that solves the 1-D radial equation for the temperature field. Energy calculations include surface losses due to radiation and convection, conductive heat transfer through the mixture of gaseous and condensed phase material, and the chemistry of gasification. Gases released by bursting bubbles determine the mass loss rate from the sample.