Ultra porous and flexible PET/Aerogel blankets were prepared at ambient pressure, and their acoustic and thermal insulation properties were characterized. Two methods were selected for the preparation of PET/Aerogel blanket. Method I was a direct gelation of silica on PET. PET non-woven fabric was dipped and swelled in TEOS/ethanol mixture, and pH of reaction media was controlled to 2.5 using HCl to promote hydrolysis. After acid hydrolysis, pH was controlled to 7,8,9, and 10 with $NH_4OH$ for the condensation. Method II was by the dipping of PET non-woven fabric in the dispersion of Silica hydrogel. The gelation process was same with Method I. However, PET fabric was not dipped in reaction media. After the hydrogel was dispersed and aged in EtOH for 24 hrs, then, PET non-woven fabric was dipped in the dispersion of hydrogel/EtOH for 24 hrs. The surface modification was carried out in TMCS/n-hexane solution, then the blanket was washed with nhexane and dried at room temperature to prevent the shrinkage. The silica areogels synthesized in optimum conditions exhibit porous network structure. Silica aerogel of highly homogeneous and smallest spherical particle clusters with pores was prepared by gelation process at pH 7. When direct gelation of silica was performed in PET nonwoven matrix (Method I), silica aerogel clusters were formed efficiently surrounding PET fibers forming network structure. The existence of a great amount of silica aerogel of more homogeneous and smaller size in the cell wall material has positive effect on the sound absorption and thermal insulation.