The gas permeability and strength properties of the concrete and cement mortar with three different dosages of polypropylene fibers were tested. The obtained results confirm a significant influence of the fibers on the increase of permeability of cement-based materials heated above 180°C. At the same time, no influence of the polypropylene fibers content on the compressive and flexural strengths, and the fracture energy of the heated cement composites was observed. The measured material parameters were used in the computer simulations of complex physical phenomena in heated concrete, confirming efficiency of the polypropylene fiber admixture in reducing pore pressure in the material exposed to fire conditions.