The thermal characteristics of sea ice are important for global climate models. The heat capacity is an equilibrium property (that is, it can be measured by comparisons of ice equilibrated at two different temperatures), and is quite well understood (Schwerdtfeger, 1963; Ono, 1966; Yen, 1981). Less well-known is the thermal conductivity of sea ice, which is a dynamic property, requiring temperature gradients across the ice. Models of thermal conductivity depend on the geometry of the constituent brine and ice components, with parallel and series models giving different thermal conductivities (Schwerdtfeger, 1963; Untersteiner, 1986, Section 10.3; Yen, 1981). Since the thermal conductivity of brine is less than that of pure ice, the parallel transport model predicts the largest value, less than but close to that of pure ice, and falling below this value for higher temperatures and larger volumes of brine. The possibility of convection within brine pockets, and of migration of the brine through the ice, has been ignored in these models.