Annular barrier

An annular barrier for providing zonal isolation in an annulus downhole between a well tubular metal structure and another well tubular metal structure or a wall of a borehole, comprising:

• a tubular metal part configured to be mounted as part of the well tubular metal structure, the tubular metal part having an outer face, an opening and an axial extension along the well tubular metal structure,
• an expandable metal sleeve surrounding the tubular metal part, the expandable metal sleeve having a circumferential groove, a first end and a second end, each end of the expandable metal sleeve being connected with the outer face of the tubular metal part, wherein the expandable metal sleeve defines an expandable space being in fluid communication with the opening in the tubular metal part for fluidly expanding the expandable metal sleeve from a first radial position to a second radial position that is different than the first radial position, and
• a sealing unit arranged in the circumferential groove, the annular sealing unit comprising an annular sealing element and a back-up sealing element abutting and supporting the annular sealing element,
• wherein the annular sealing element in a cross-section along the axial extension has a first width, a second width and a third width;
• the second width is larger than the first width and the third width and is arranged between the first width and the third width;
• the back-up sealing element has a first contact area, and the annular sealing element has a second contact area, where the first contact area has a shape that mates with the second contact area,
• wherein the back-up sealing element has a first face part and a second face part forming the first contact area of the back-up sealing element;
• the first face part inclines and faces away from the groove, and the second face part inclines and faces towards the groove.