In this work a three dimensional heat transfer analysis of honeycomb Transparent Insulation Materials (TIM) destined for improving the efficiency of flat plate solar collectors is performed. The cellular and repetitive nature of the TIM structure has allowed simplify the problem and simulate a single isolated cell with opaque and adiabatic walls. The combined heat transfer by radiation and conduction across the isolated cell is treated by means of the solution of the energy equation in its three dimensional form which is coupled to the Radiative Transfer Equation (RTE). The Finite Volume Method is used for the resolution of the RTE. The numerical results are compared to experimental measurements of the heat transfer coefficient on various honeycomb TIM given by different authors in the literature showing a reasonable agreement. The 3D simulations have allowed to study in detail the thermal behavior of the TIM and to understand the real physics of the problem. Finally, a parametric study is conducted in order to investigate the effect of the variation of the most relevant optical and dimensional parameters of the TIM on the heat transfer. (C) 2014 Elsevier Ltd. All rights reserved.