Closing system for refrigerators, comprising: - at least one fixed frame suited to be attached to the opening of a refrigerator (F) and defining an opening designed to give access to the internal volume of said refrigerator (F); - at least one door associated with said fixed frame , said at least one door being movable with respect to said fixed frame between a closed configuration, in which said door is closed on said fixed frame , and an open configuration, in which said door is open on said fixed frame , said at least one door comprising a door frame and a panel fixed to said door frame , preferably made of a transparent material, wherein said fixed frame and said door frame are made of high density polyurethane by means of moulding techniques; characterized in that said at least one fixed frame comprises a plurality of fixing bodies arranged on the uprights of said at least one fixed frame , said fixing bodies being configured to be attached to the frame (T) of said refrigerator (F) and/or to corresponding fixing bodies of a contiguous fixed frame of said closing system , said fixing bodies being made of said high density polyurethane by means of moulding techniques to promote high thermal insulation between the frame (T) of the refrigerator (F) and the environment outside the closing system . - at least one fixed frame suited to be attached to the opening of a refrigerator (F) and defining an opening designed to give access to the internal volume of said refrigerator (F); - at least one door associated with said fixed frame , said at least one door being movable with respect to said fixed frame between a closed configuration, in which said door is closed on said fixed frame , and an open configuration, in which said door is open on said fixed frame , said at least one door comprising a door frame and a panel fixed to said door frame , preferably made of a transparent material, wherein said fixed frame and said door frame are made of high density polyurethane by means of moulding techniques; characterized in that said at least one fixed frame comprises a plurality of fixing bodies arranged on the uprights of said at least one fixed frame , said fixing bodies being configured to be attached to the frame (T) of said refrigerator (F) and/or to corresponding fixing bodies of a contiguous fixed frame of said closing system , said fixing bodies being made of said high density polyurethane by means of moulding techniques to promote high thermal insulation between the frame (T) of the refrigerator (F) and the environment outside the closing system . wherein said fixed frame and said door frame are made of high density polyurethane by means of moulding techniques; characterized in that said at least one fixed frame comprises a plurality of fixing bodies arranged on the uprights of said at least one fixed frame , said fixing bodies being configured to be attached to the frame (T) of said refrigerator (F) and/or to corresponding fixing bodies of a contiguous fixed frame of said closing system , said fixing bodies being made of said high density polyurethane by means of moulding techniques to promote high thermal insulation between the frame (T) of the refrigerator (F) and the environment outside the closing system . <EOS>