PURPOSE: To provide a flexible filling material with heat insulation effect by placing a heat insulation material consisting of a mineral fibrous material and a granular material opposite to a slidable plate fixed in a sheet jacket by supporting and holding members.

CONSTITUTION: A support web 7 has a shape to generate the self-stress, and is set to the inside of a sheet jacket 5 after an inner surface of the sheet jacket 5 is covered by a heat resistant mat 6 in advance. After a mineral fiber 13 is filled into a chamber between the support webs 7, a constitution unit composed of a slidable plate 8 and a piercing sleeve 11 in advance, is set to the sheet jacket 5 so that a slidable surface 9 of the slidable plate 8 is located at an edge part 14 of a peripheral sheet 4. As a result, the slidable plate 8 is fixedly surrounded by the peripheral sheet 4. The excellent heat insulation effect on the slidable plate 8 set together with the piercing sleeve 11 is achieved during the operation by a body comprising the sheet jacket 5 which is covered by the mat 6 and provided with the support webs 7, and the mineral fiber 13.