PURPOSE: To improve the heat resistance and the executability by mixing a specific wt.% of a glass fiber cut in a predetermined length with rock wool fiber having a specific mean fiber size and containing composition, gathering them, forming it in a felt sheet state by needling, providing mat having a specific density, and providing an aluminum layer on the outer periphery.

CONSTITUTION: A coating tube comprises a mat provided on the outer periphery of a cylindrical tube and having a thickness of 10 to 20mm, and an aluminum layer provided on the outer periphery of the mat. The mat contains an ore as a main material, and silicon oxide, aluminum oxide, calcium oxide, magnesium oxide, iron oxide, and sodium oxide of specific wt.%. Glass fiber cut in a predetermined length of 10wt.% or more is mixed with a rock wool fiber having a mean fiber size of 4 to 7μm, gathered, and formed in a felt sheet state by the needling step 5, and so compressed and laminated that the density becomes 150 to 300kg/m3.