The paper investigates dynamic processes occuring in porous polymer materials under the action of impulse thermal radiation that lead to polymer pyrolysis with generation of gases in its pores. The new theory is developed for averaging the processes in porous multiphase media that describes not only processes averaged over phases but also microprocesses inside each phase. The dynamic problem statement is given for deforming and heat-mass-transfer in polymer materials with the pyrolysis effect under thermal irradiation. Computations are performed for the problem on the effect of radiation on a plate. It is shown that the pyrolysis of a polymer matrix leads to an appearance of additional impulses of intrapore gas pressure and, thus, considerably redistributes a wave picture in the porous polymer material.