PURPOSE: To compose a light and very strong insulated base board with a reinforced layer formed on the top of a plastics foamed member by laminating a non-foamed sheet of hard plastics.

CONSTITUTION: An interior ceiling 10 is produced as followed; The top of a base board 11 made of a plastics foamed material is adhesively laminated with a non- foam sheet of hard plastics and subsequently a breathing soft plastics foamed material. Then, the surface of the product thus obtained is coated with a decorating material 14. The base member 11 mainly acts as an insulator. The hard plastics non-foamed sheet 12 functions as a reinforced layer for the base member 11 with the foamed member 13 mainly having both buffer and insulation effects 1ong with a sound absorption effect. The surface decorating material improves sound absorption property.