Although by no means a new development, the insulation of fresh concrete as a means of protecting it from freezing is commanding more attention now than ever before. Batt insulation has been used to a considerable extent as a means of protecting concrete from freezing temperatures but with the serious limitation of the inability of the liners that enclose the insulation material to stand up under rough handling. This has been overcome by the development of special blanket insulation products, made of balsam wool, glassfiber, or rock wool, specifically designed for the job of protecting exposed concrete. Liners are more frequently made of asphalt-saturated and coated heavy kraft paper and flanges are usually provided to facilitate fastening the blankets to the forms. The economy of using insulation to protect winter concrete results form the fact that it helps retain not only the heat of the material at the time it is placed but also the considerable amount of heat that is released as the cement hydrates. Winter concrete protected with insulation also has a potential quality advantage. Protecting concrete with dry heat also exposes it to the additional moisture the air can hold as it is heated; a problem in summer that with heaters can be created artificially in winter. The cost of protecting concrete with insulation as compared with other methods is also substantially lower. Some contractors report that insulating either flatwork or forms costs only half as much as providing equivalent protection with heated enclosures and watchmen for fire protection.