The invention relates to a molding device (1) for receiving fibers onto which a resin is injected, including a base (3), side plates (5) confining the base (3), and a cover (7) capable of engaging with a free end (9) of the side plates (5) in order to define an inner space (11) for receiving the fibers and the resin, wherein said device (1) comprises, in the inner space (11), a skin (21) that is configured to be complementary to the inner surface of the cover (7) and to at least a portion of the inner surface of the side plates (5). The invention also relates to a method for manufacturing a resin part using such a device (1).