Free volume distribution was studied for polyurethane networks differing in the molecular mass of oligopropylene glycol taken in the synthesis. To estimate the free volume distribution experimentally, inversed gel chromatography was proposed. The integral and differential distribution of the free volume was constructed. Experimental data for the crosslinked polyurethanes showed the difference in the value of the free volume and its distribution due to the varied packing of oligomeric chains in the regions of the molecular mass below and above the critical molecular mass of entanglements.