A method of making a thermally insulated sandwich polyurethane (PUR) shipper for a temperature sensitive payload is provided. The method comprises the steps of mounting an inner box upside down on a tool, adhering an insulating panel to the outer facing surfaces of the inner box, positioning an outer box around the inner box assembly, pouring liquid polyurethane into the gap between the outer box and inner box assembly, and foaming the liquid polyurethane. The PUR foam fills the space between the VIP panels and the outer box, and preferably covers the VIP panels.