The present invention relates to an open-cell foam, and to a process for producing this open-cell foam by melting a thermoplastic, or a mixture comprising a thermo-plastic, giving a melt, mixing the melt with at least one blowing agent under pressure, and foaming the melt comprising the blowing agent via extrusion into the free atmosphere, the temperature of the melt during the foaming process being greater than the melt temperature at which a closed-cell foam is formed, and/or adding a pulverulent solid, and/or adding a foreign polymer. The present invention further relates to the use of the foam of the invention for sound deadening or for producing materials by sound deadening.