The conductors represent thermal paths. The nodes represent isothermal surfaces. Each conductor is connected to two nodes. Each node is connected to one or more conductors. Conductors model both radiative and conductive thermal paths.
Nodes are either standard nodes or boundary nodes.
Boundary nodes are those which represent thermal sources or sinks such as cryogen reservoirs. The thermal conductivity k depends on the material and the temperature range spanned by the conductor. The effective emissivity depends on the emissivities of the surfaces and the number of MLI layers. The effective area depends on the view factor of the two surfaces. In the case of regular, non-boundary nodes, the heat flowing into the node should equal the heat flowing out of the node.