Variation of heat conductivity K with porosity φ. The results for fine-grained silica powder (filled circles) from experiments of Krause et al. (2011a,b), and for particulate basalt (crosses) from Fountain & West (1970). The typical grain size is indicated for both cases. Open squares and open circles are experimental results for heat-conductivity and porosity for ordinary H and L chondrites, respectively, from (Yomogida & Matsui 1983). The solid line is an analytical fit to the data, according to Eq. (30).