In connection with a study of the emissivity of metals at low temperatures, a quantitative analysis has been made of the factors involved in the design of storage containers for liquid helium. Experiments confirm the analysis, which has resulted in an exceedingly simple liquid‐nitrogen‐protected liquid helium container having a helium evaporation rate of 1 percent per day.The hemispherical emissivity of mechanically polished copper at 4.23°K was determined for blackbody radiation. For radiation corresponding to that emitted by a blackbody at 77.1°K and 297.1°K, the measured emissivities are 6.9×10−3and 1.29×10−2, respectively. These data are discussed in relation to the recent theoretical work of Reuter and Sondheimer.The heat of vaporization of helium at 4.228°K was determined to be 4.93 cal g−1, in substantial agreement with the data of Dana and Kamerlingh Onnes. Kistemaker's thermodynamic considerations questioning the accuracy of these data are evaluated in terms of the new determination.