o, m, p-xylene, p-dichlorobenzene, 1,2,4 trichlorobenzene and naphthalene were calibrated as condensates used in thermoporosimetry technique. Exponential relationships were found connecting the pore radii (Rp(nm)) and ΔT (C °) on one side and the apparent energy of crystallization (Wa (J.cm-3)) and ΔT on the other side: Pore or mesh size distribution can be derived from DSC thermal recording using the following equation: All the numerical parameter values were determined. Polyethylene and polypropylene samples, cross-linked with high-energy electrons or γ-rays, were submitted to thermoporosimetry study. The mesh size distributions (MSD) calculated for these polyolefins, using o, m and p-xylene as solvent, were found in the same sequences that their degrees of swelling and the irradiation doses they received.