<p>A microporous soundproofing material constituted of an expanded material formed through the step of impregnating a thermoplastic elastomer with an inert gas at a high pressure and then decompressing the impregnated elastomer. The soundproofing material has a high characteristic impedance, is clean and lightweight, and has excellent flexibility. This microporous soundproofing material includes: a microporous soundproofing material which is constituted of an expanded material formed through the step of impreganting an unexpanded molding comprising a thermoplastic elastomer with an inert gas at a high pressure and then decompressing the impregnated molding; and a microporous soundproofing material which is constituted of an expanded material formed by impregnating a molten thermoplastic elastomer with an inert gas at a high pressure and then subjecting the impregnated elastomer to molding simultaneously with decompression.</p>
