Liquid helium is stored in containers fitted with 7 cm-thick "superinsulation" consisting of a large number of layers of very thin aluminized Mylar sheets. The rate of evaporation of liquid in a 200 L container is about 0.7 L per day. Assume that the container is spherical and that the external temperature is 20 C. The specific gravity of liquid helium is 0.125 and the latent heat of vaporization is 21kj/kg. Estimate the thermal conductivity of superinsulation.

Question