Apparatus for sound insulation of a machine, with - a sleeve which has a sound-absorbing composite material wall with a plastic carrier layer with a Shore-A-hardness in the range from 66 to 90, in particular in the range from 70 to 85, as outer layer and a sound-absorbing layer as inner layer, - wherein the composite material wall has two edge regions (22, 24) which lie against and/or above one another and each have a boundary edge (18, 20) which can be connected to one another and/or to one another by means of at least one plug-in connection arrangement, - wherein the at least one plug-in connection arrangement has a plug-in tab arranged in the one first edge region of the composite material wall and a receiving element which is arranged in the other second edge region of the composite material wall and into which the plug-in tab can be plugged, - characterized in that the plug-in tab has a web which has an end connected to the plastic carrier layer and an end section facing away from this end with an insertion end and an upper side and a lower side, - wherein the web has at least one locking recess on the underside of its end portion, and - wherein the receiving element of the at least one plug-in connection arrangement has an insertion opening facing the first edge region for the insertion end and at least a part of the end portion of the web of the plug-in tab and a locking projection arranged in front of the insertion opening in the second edge region as viewed in the direction of insertion of the plug-in tab into the insertion opening, which, when the insertion end of the web of the plug-in tab is received by the insertion opening, is immersed in the locking recess on the underside thereof. - a sleeve which has a sound-absorbing composite material wall with a plastic carrier layer with a Shore-A-hardness in the range from 66 to 90, in particular in the range from 70 to 85, as outer layer and a sound-absorbing layer as inner layer, - wherein the composite material wall has two edge regions (22, 24) which lie against and/or above one another and each have a boundary edge (18, 20) which can be connected to one another and/or to one another by means of at least one plug-in connection arrangement, - wherein the at least one plug-in connection arrangement has a plug-in tab arranged in the one first edge region of the composite material wall and a receiving element which is arranged in the other second edge region of the composite material wall and into which the plug-in tab can be plugged, - characterized in that the plug-in tab has a web which has an end connected to the plastic carrier layer and an end section facing away from this end with an insertion end and an upper side and a lower side, - wherein the web has at least one locking recess on the underside of its end portion, and - wherein the receiving element of the at least one plug-in connection arrangement has an insertion opening facing the first edge region for the insertion end and at least a part of the end portion of the web of the plug-in tab and a locking projection arranged in front of the insertion opening in the second edge region as viewed in the direction of insertion of the plug-in tab into the insertion opening, which, when the insertion end of the web of the plug-in tab is received by the insertion opening, is immersed in the locking recess on the underside thereof.