A spacer for insulated glass units includes a main body co-extruded from first and second plastics, the second plastic having lower thermal conductivity and higher flexibility than the first plastic. The main body includes first and second side walls arranged parallel to each other, a glazing interior wall connecting to the side walls, an outer wall, which is arranged substantially parallel to the glazing interior wall and connects the side walls to one another directly or via connecting walls, and a cavity, which is enclosed by the side walls, the glazing interior wall, and the outer wall or by the side walls, the glazing interior wall, the outer wall, and the connecting walls. The main body is designed as a hollow profile formed from the second plastic, in which hollow profile the first plastic is arranged, at least in some regions, on the inside directly adjacent the hollow profile.