A panel for an air treatment unit or an air treatment system, the panel being shaped by sheet metal walls, said walls comprising an outer metal sheet and an inner metal sheet laid one on top of the other at a certain distance, forming the two front faces of the panel and a side wall (203, 204, 205, 206) of metal sheet in such a way as to internally define a containing space suitable for containing a filler material, for example a foam material such as polyurethane or a solid material such as rock wool; - the panel comprising one or more element/s (30, 330) made of thermally insulating material arranged in such a way as to generate a discontinuity of material in one or more areas of said sheet metal walls constituting the panel and thus generating an interruption and/or a reduction of heat transmission along the sheet metal walls in the arranged area(s); - wherein said one or more element/s is/are arranged in at least one part of the side wall of said panel in such a way as to generate said discontinuity of material in said part of the side wall where it is/they are arranged and generating said interruption and/or reduction of heat transmission between the outer metal sheet and the inner one and/or vice versa; - wherein said at least one part of said side wall forms an opening which creates a separation zone between the outer metal sheet and the inner metal sheet; - and wherein said one or more element/s (30, 330) made of thermally insulating material is/are arranged in correspondence with said opening so as to close said opening in such a way that said element/s creates /create said interruption and/or a reduction of the passage of heat between the outer metal sheet and the inner one and/or vice versa; characterized in that: - At least the side wall part of the panel comprising said thermally insulating element (30, 330) forms a seat positioned at a different height from the opening for arranging said element (30, 330) and with said seat suitable for accommodating a profile (50; 350) in such a way that said profile is at least partially covered by said panel, the profile preferably being metallic, for example extruded aluminum. - the panel comprising one or more element/s (30, 330) made of thermally insulating material arranged in such a way as to generate a discontinuity of material in one or more areas of said sheet metal walls constituting the panel and thus generating an interruption and/or a reduction of heat transmission along the sheet metal walls in the arranged area(s); - wherein said one or more element/s is/are arranged in at least one part of the side wall of said panel in such a way as to generate said discontinuity of material in said part of the side wall where it is/they are arranged and generating said interruption and/or reduction of heat transmission between the outer metal sheet and the inner one and/or vice versa; - wherein said at least one part of said side wall forms an opening which creates a separation zone between the outer metal sheet and the inner metal sheet; - and wherein said one or more element/s (30, 330) made of thermally insulating material is/are arranged in correspondence with said opening so as to close said opening in such a way that said element/s creates /create said interruption and/or a reduction of the passage of heat between the outer metal sheet and the inner one and/or vice versa; - At least the side wall part of the panel comprising said thermally insulating element (30, 330) forms a seat positioned at a different height from the opening for arranging said element (30, 330) and with said seat suitable for accommodating a profile (50; 350) in such a way that said profile is at least partially covered by said panel, the profile preferably being metallic, for example extruded aluminum.