Abstract: A roof box comprising: (a) a bottom part comprising a bottom section and side sections projecting upwardly from the bottom section, the bottom section being adapted for mounting the roof box to a roof area of a vehicle; (b) a top part movable relative to the bottom part between an opened position and a closed position, the top part comprising a top section and side sections projecting downwardly from the top section, wherein, in the closed position, the bottom section and the side sections of the bottom part and the top section and the side sections of the top part define an internal volume for storing objects in the roof box, the top part comprising first and second polymeric walls joined together at the side sections of the top part to define an interior space between the first and second polymeric walls; and (c) at least one strengthening element provided in the top section of the top part, each strengthening element being made of a respective portion of the first polymeric wall fused to a corresponding po