The problem confronting the refinery engineer in the selection, application, and maintenance of an insulation for low-temperature service involves consideration of factors that are, in general, of only minor significance in the high-temperature field. The principal basic factor in any insulation is, of course, conductivity. However, water absorption, upper-temperature limit, fire resistance, coefficient of expansion, and so on, also must be considered in selecting an insulant for particular service conditions. This paper presents a discussion of the more common insulating materials and the relative importance of the various properties and characteristics of these materials for low-temperature service in petroleum refineries. In addition to the care exercised in obtaining the proper insulating material, considerable attention must be devoted to the selection of accessory materials such as adhesives, vapor sealers, water and fireproof coverings, mechanical securement devices, and the like. These materials also will be discussed since they have a pronounced effect on the over-all effectiveness and life of the insulation.