Since wood is porous it also is a good heat and sound insulating material. Puffing the cell wall may lose certain level of mechanical properties but would increase its insulation properties. In this study, Trema orientalis wood was first treated with nitric acid aqueous solution to damage the S3 layer of cell walls, followed by puffing the cell wall inward with saturated urea and ZnCl2 solutions. Results indicated that treating Trema orientalis with 10% nitric acid at 100 oC for 20 minute damaged the S3 layer of cell walls, and the subsequent treatment with urea and ZnCl2 saturated solutions caused the fiber tracheid walls to swell up to 76%. Then, the swollen material was dried with critical CO2 fluid to obtain puffed wood. SEM examinations of nitric acid-treated samples showed that lignin were removed from the S3 layer surfaces and S3 mirofibrils were ruptured causing the entire secondary walls to swell inward.