As a basic expriment to find out the thermal insulation effect of bedding KES-F7 was used to measure. The warmth retaining ratio of the six kinds of filling materials as cotton, wool, silk, down, cotton; polyester was measured, and the infleunce on the warmth retaining ratio of the warmth retaining ratio and humidity by the material was investigated. The results obtained are as follows: 1. The warmth retaining ratio of each filling material was shown to range from 70% to 77%. The warmth retaining ratio of each material proved to be high in order down>polyester> cotton/polyester> cotton > silk > wool fiber. 2. The warmth retaining ratio of each filling material decreased with the increse of the humidity. The effective reduction rate by filling fiber`s was high in order wool>cotton> cotton/polyester>silk>down>polyester material. 3. The warmth retaining ratio of each filling material was shown to be in counter-correlation with the humidity, and the correlation coefficient (r=0.94-0.98) proved to be highly significant.