This study was performed to investigate the thermal and the warmth retaining properties of non-woven fabrics by comparing it with changing factor of packing density. The results are summarized as follows. 1. There is a great deal a difference between the temperature of heat plate and that of high temperature surface of non-woven fabric. And then, it is more desirable to apply the temperature of high-temperature surface of non-woven fabric than that of heat plate to compute the thermal conductivity. 2. The thermal conductivity of non-woven fabric diminish little by little as packing density increases, but after the limit packing density, pc=0.02g/㎤, the thermal conductivity is almost definitely maintained. 3. The warmth retaining property of non-woven fabric increases as packing density increases, but after the limit packing density, the thermal resistance is almost definitely maintained.