To provide a sleeve forming sheet which makes a sheet body formed in a shape along a peripheral surface of a fire compartment section and which can facilitate the operation of arranging the sheet body in a through-hole and the operation of forming a penetration portion structure; and to provide a formation method for the penetration portion structure.

The sleeve forming sheet 20 is arranged outside a thermally expansible refractory material 15 so as to form the penetration portion structure T in a refractory cavity wall W. The sleeve forming sheet 20 is equipped with the sheet body 21 which is composed of a glass cloth (nonmetallic material) with noncombustibility and which has flexibility so as to be deformable along a peripheral wall surface 11b of a partition wall 11.