An internal combustion engine exhaust system muffler (1) has a housing (2) within which two chambers (3) are formed with an inner panel (4) arranged therebetween. The inner panel (4) has at least one collar (8) at the edge, which has an outer side (9) facing the housing (2), and wherein the housing (2) has, on an inner side (11), in the area of the inner panel (4), at least one contour (12), which faces the collar (8) and with which the collar (8) is in contact. Reduced noise generation, reduced wear as well as prolonged service life can be achieved with the outer side (9) of the collar (8) forming a cone structure (10) in profile and the contour (12) of the housing (2) forms a cone structure seat (13) with a complementary cone profile and with which the cone (10) is flatly and non-positively in contact.