A cooler, preferably a gas cooler for a cooling system, comprising an inlet zone and an outlet zone of the cooling medium, each of which contains a set of flat tubes parallel to each other and an inlet/outlet manifold and an inner manifold (lb), wherein said flat tubes of the inlet and outlet zones (I,II) are connected at opposite ends to the inlet/outlet manifolds and the inner manifold for supplying from the inlet zone, guiding it to the outlet zone and discharging it from the outlet zone, wherein each of said manifolds (1a,1b)comprises: a inner housing (4,4') having a closed profile and having at least one longitudinal channel defined therein and having a plurality of slots on one of its surfaces being in fluid communication to said at least one longitudinal channel; and a cover (2,2') applied on said inner housing (4,4') and having a plurality of slots located at positions corresponding to the positions of said slots of said inner housing (4,4') for introduction flat tubes of the cooler to them, characterised in that it comprises an insulating tube having first and second ends and disposed between the inlet and outlet zones (I,II) of the cooling medium, and extended at its first end longitudinally to said flat tubes of the zones (I, II) to separate and isolate the cooler zones, an inlet/outlet manifold comprising two segments (4a, 4b)of the inner housing, said segments (4a,4b) having the inner ends facing each other, and said inner ends are closed by means of baffles and are arranged at a distance to each other, and the cover mounted on said inner housing in the form of one part, having a central slot formed and arranged for receiving the first end of said insulating tube and placing it between the segments (4a, 4b) of the inner housing; wherein said second end of the insulating tube is located in front of outer surface of said cover of said inner housing of the inner manifold. a inner housing (4,4') having a closed profile and having at least one longitudinal channel defined therein and having a plurality of slots on one of its surfaces being in fluid communication to said at least one longitudinal channel; and a cover (2,2') applied on said inner housing (4,4') and having a plurality of slots located at positions corresponding to the positions of said slots of said inner housing (4,4') for introduction flat tubes of the cooler to them, characterised in that it comprises an insulating tube having first and second ends and disposed between the inlet and outlet zones (I,II) of the cooling medium, and extended at its first end longitudinally to said flat tubes of the zones (I, II) to separate and isolate the cooler zones, an inlet/outlet manifold comprising two segments (4a, 4b)of the inner housing, said segments (4a,4b) having the inner ends facing each other, and said inner ends are closed by means of baffles and are arranged at a distance to each other, and the cover mounted on said inner housing in the form of one part, having a central slot formed and arranged for receiving the first end of said insulating tube and placing it between the segments (4a, 4b) of the inner housing; wherein said second end of the insulating tube is located in front of outer surface of said cover of said inner housing of the inner manifold.