To make existence and capacity of a synthetic resin layer serving as an interlayer easily discernible at a vegetable and fruit market or the like by making the synthetic resin layer formed of synthetic resin emulsion colored.

Paper layers 6 are stuck together with a colored synthetic resin layer 8 interposed in between, and thereby a multilayer paper 1 is formed. Paper to be used for forming the paper layers 6 of the multilayer paper 1 are liner and a corrugating medium generally used for making corrugated board. Synthetic resin such as styrene-butadiene resin is used solely, or in a multiple mixture, for making synthetic resin emulsion forming the interlayer for the multilayer paper 1. Nitroso dye or the like is used as a dye for coloring the synthetic resin layer 8. Coating is made, if necessary, at the surface of the corrugated board sheet with a substance having a low heat radiation mainly composed of aluminum power and/or white pigment, and thereby absorption of radiant heat is decreased and heat-insulating effect is heightened further.