A foaming system for foaming cabinets of electrical household appliances, comprising - a conveying line of a shell and a cabinet of electrical household appliance, - a holding apparatus equipped with outer abutting assembly and internal abutting assembly, arranged to keep coupled said cabinet and shell of electrical household appliance, during a foaming operation, - foaming injectors mounted at least vertically movable, to enter a gap between cabinet and shell of a household electrical appliance, said holding apparatus, comprising a frame whereon there are supported, mutually movable in a vertical direction, said outer abutting assembly and said underlying internal abutting assembly, defining a retaining jig which acts as abutting means to keep coupled said cabinet and shell of electrical household appliance between which a gap is defined, wherein said outer abutting assembly consists of moving walls of a generally parallelepipedal formwork and said inner abutting assembly is in the form of a variously shaped plug component, characterised in that said outer abutting assembly has a back cap sub-assembly mounted pivoting on said frame according to a horizontal axis, between an operating position to close said jig and a waiting position rotated by at least about 90° whereby at least part of said gap within said jig is made accessible, said back cap sub-assembly being a portion consisting of a back retaining cap mounted pivoting according to a horizontal rotation axis, which makes up a movable sub-portion of the movable outer abutting assembly which can open/close fold-like with respect to the remaining part of said outer abutting assembly. - a conveying line of a shell and a cabinet of electrical household appliance, - a holding apparatus equipped with outer abutting assembly and internal abutting assembly, arranged to keep coupled said cabinet and shell of electrical household appliance, during a foaming operation, - foaming injectors mounted at least vertically movable, to enter a gap between cabinet and shell of a household electrical appliance, said holding apparatus, comprising a frame whereon there are supported, mutually movable in a vertical direction, said outer abutting assembly and said underlying internal abutting assembly, defining a retaining jig which acts as abutting means to keep coupled said cabinet and shell of electrical household appliance between which a gap is defined, wherein said outer abutting assembly consists of moving walls of a generally parallelepipedal formwork and said inner abutting assembly is in the form of a variously shaped plug component, characterised in that said outer abutting assembly has a back cap sub-assembly mounted pivoting on said frame according to a horizontal axis, between an operating position to close said jig and a waiting position rotated by at least about 90° whereby at least part of said gap within said jig is made accessible, said back cap sub-assembly being a portion consisting of a back retaining cap mounted pivoting according to a horizontal rotation axis, which makes up a movable sub-portion of the movable outer abutting assembly which can open/close fold-like with respect to the remaining part of said outer abutting assembly.