Sheet member, forming method of the same, exhaust gas treatmenet apparatus, and muffling apparatus

摘要

A sheet member including inorganic fibers includes a first outer layer; a center layer; and a second outer layer. The first outer layer, the center layer, and the second outer layer are laminated with each other such that both the first and the second outer layers are outermost layers; the center layer includes inorganic fibers having diameters equal to or less than approximately 3 micrometers; and the first and the second outer layers include inorganic fibers having diameters greater than approximately 3 micrometers.