A composite sheet comprising an upper layer 2 and a lower layer 3 both made of a substantially inextensible sheet which are partially bonded to each other at a large number of joints 4. The upper layer 2 forms a large number of outward hollow projections 5 in the area other than the joints 4. The projections 5 and the joints 4 are arranged such that the projections and the joints alternate in one direction to make lines and that the projections in each of the lines are out of alignment with the projections in the adjacent lines.