Abstract: The panel system is meant for construction of a panel fillet or a major panel surface to be mounted in a pitched roof or in a facade, comprising a number of fixed panels (1) together with a number of openable panels (2), each panel comprising a frame structure composed of frame members (13, 22) bordering a panelling element (32) between them, each frame member (13, 22) comprising a profile element (30) and at least a core element (35). The profile elements (30) are designed as uniform standard parts, and in that at least some frame members of the frame structure are provided with means to vary the moment of inertia, where the means can comprise at least one element (47) which is received in said core element (35) and which extend over essentially the entire length of the frame member.