A pallet shipper for shipping a temperature sensitive payload, the pallet shipper characterised in that it comprises: a rectangular base comprising a rectangular upper portion and a rectangular lower portion located adjacent to and located under the upper portion, the upper portion having a peripheral ledge extending outward beyond the lower portion, the ledge having an underside that slopes downward toward the lower portion; two L-shaped, unitary, first corner structures, each first corner structure comprising a grooved panel and a first flanged panel orthogonal to the grooved panel, the grooved panel and the first flanged panel joined along a vertical corner, the first corner structure comprising an inwardly extending L-shaped footer near a bottom edge, the grooved panel extending from the vertical corner to a distal grooved edge, the distal grooved edge defining a vertically oriented groove, the first flanged panel extending from the vertical corner to a distal flanged edge and having a first flange extending from the distal flanged edge in a direction away from the vertical corner; and two L-shaped, unitary, second corner structures, each comprising a tongued panel and a second flanged panel orthogonal to the tongued panel, the tongued panel and the second flanged panel joined along a vertical corner, each second corner structure extending from a bottom edge to a top edge, each second corner structure comprising an L-shaped footer extending inwardly from the tongued panel and the flanged panel near the bottom edge, the tongued panel extending from the vertical corner to a distal tongued edge, a tongue extending outwardly from the distal tongued edge in a direction away from the vertical corner, the second flanged panel extending from the vertical corner to a distal flanged edge and having a second flange extending from the distal flanged edge in a direction away from the vertical corner; wherein each groove is configured to receive a tongue to form a tongue and groove seam; and each first flange is configured to mate with a corresponding second flange to form a convoluted seam. a rectangular base comprising a rectangular upper portion and a rectangular lower portion located adjacent to and located under the upper portion, the upper portion having a peripheral ledge extending outward beyond the lower portion, the ledge having an underside that slopes downward toward the lower portion; two L-shaped, unitary, first corner structures, each first corner structure comprising a grooved panel and a first flanged panel orthogonal to the grooved panel, the grooved panel and the first flanged panel joined along a vertical corner, the first corner structure comprising an inwardly extending L-shaped footer near a bottom edge, the grooved panel extending from the vertical corner to a distal grooved edge, the distal grooved edge defining a vertically oriented groove, the first flanged panel extending from the vertical corner to a distal flanged edge and having a first flange extending from the distal flanged edge in a direction away from the vertical corner; and two L-shaped, unitary, second corner structures, each comprising a tongued panel and a second flanged panel orthogonal to the tongued panel, the tongued panel and the second flanged panel joined along a vertical corner, each second corner structure extending from a bottom edge to a top edge, each second corner structure comprising an L-shaped footer extending inwardly from the tongued panel and the flanged panel near the bottom edge, the tongued panel extending from the vertical corner to a distal tongued edge, a tongue extending outwardly from the distal tongued edge in a direction away from the vertical corner, the second flanged panel extending from the vertical corner to a distal flanged edge and having a second flange extending from the distal flanged edge in a direction away from the vertical corner; wherein each groove is configured to receive a tongue to form a tongue and groove seam; and each first flange is configured to mate with a corresponding second flange to form a convoluted seam.