One of the most important factor for the comfort of the passenger vehicles is the minimization of the compressible transmissibility during the running vehicles. Seat foam materials of I2 series(index 95 and the contents of isocyanate TDI was changed in percentages 75, 70, 65, 60, 50, 40) and DI series(density 50kg/$ extrm{m}^3$, index was changed 100, 95, 90) showed the significant differences in their transmissibility depended upon their chemical constitution such as index and contents of isocyanate TDI. The minimum trasmissibility of seat foam materials of I2 series was found from the materials with the contents of 65% isocyanate TDI and the index 95 at the frequency 4.79~5.31Hz. Also the minimum transmissibility of seat foam materials of DI series was found from the materials with the index 90 and the density of 50kg/$ extrm{m}^3$ at the frequency of 4.79~5.31Hz.