Abstract: Walk-in coolers for maintaining a chamber at a temperature are assembled from sandwich panels, which are welded together in end-to-end abutting relationship. Each panel generally has an inner metallic facing and a spaced opposed metallic facing with the space between the facings filled with a thermal insulating organic material having a coefficient of thermal conductivity of less than 0.3 Btu/hr,ft.sup.2,.degree.F./ft. The abutting ends of the inner facings are welded together to cover the crevices between the inner facings and to fill the corners between mutually perpendicular facings. A heat conducting member having a coefficient of thermal conductivity greater than about 0.3 Btu/hr,ft.sup.2,.degree.F./ft is disposed in the insulating material in contact with the inner facing adjacent the welded abutting end.