A novel driven‐rod, radiant pyrolysis technique has been used to study steady‐state linear regression of vertically mounted polystyrene rods degrading under high‐flux, nonflaming conditions that simulate those of combustion. With this technique a reliable, reproducible temperature‐depth profile (identical for combustion and radiant pyrolysis) for polystyrene has been obtained and used to successfully calculate the observed mass loss rate. Residues and volatiles have been analyzed. Mechanistic treatment of these results indicates that degradation of polystyrene under these rapid‐heating conditions is similar to that under more conventional slow‐heating conditions in the absence of oxygen. Oxidation is unimportant in the condensed‐phase degradation of polystyrene in this configuration. This radiant pyrolysis technique has also been used to obtain the heat of gasification of polystyrene.