Provided is an injection molded panel having a top side and a bottom side. The panel is configured with at least an elastic portion, the elastic portion including a plurality of undulating deformable strands intersecting with one another at rigid connecting locations, the rigid connecting locations alternatingly extending at opposite sides of the panel at alternating top peaks and bottom peaks, the peaks defining together the respective top side and the bottom side.

A reinforcing member includes a plate-shaped member that is made of a fiber-reinforced resin in which a continuous fiber is used as a reinforcement fiber and that has a first surface and a second surface. The plate-shaped member includes an outer circumferential portion that defines an outer edge of the plate-shaped member, a convex portion that is convex on a side of the first surface in an area inside the outer circumferential portion, and a plurality of concave portions that are concave on the side of the first surface in an area inside the convex portion.