Our objective is to calculate and to compare the rectifying thermal coefficient of various bulk porous silicon configurations. We consider successively homogeneous devices involving two- and three elements and several graded devices characterized by variable porosity and/or size of the pores along the system. The criterion is to obtain rectifying coefficients different from one in order that thermal rectification be as efficient as possible. In that respect, it turns out that the porous bulk porous configurations are of little interest, in contrast to the bulk porous bulk systems whose rectifying coefficients may be larger than two and comparable to the values of the simpler two-element bulk porous devices. Graded systems with either a variable porosity or a variable pore size do not exhibit better results. However, when both porosity and pore size are varying along the device, the highest efficiency is obtained. (C) 2016 Elsevier Ltd. All rights reserved.