Nanoporous silicon carbide materials were prepared by the pyrolysis of the preceramic polymer, polycarbosilane (PCS), with and without the addition of an inert filler (nano- and micron-sized silicon carbide powders). Hydrosilylation crosslinking of PCs with divinylbenzene prior to pyrolysis appeared to have little influence on the development of micro- and mesoporosity. Maximum micropore volumes were 0.28 cm(3) g(-1) for non-crosslinked PCS and 0.25, 0.33 and 0.32 cm(3) g(-1) for PCS crosslinked with 2, 6 and 10 wt.% DVB respectively. Micropore volumes decreased under hydrothermal conditions to 0.03 cm(3) g(-1) for non-crosslinked and 0 cm(3) g(-1) for crosslinked PCs. Porosity was also lost at temperatures above 700 degrees C. The addition of nano-sized SiC powders to PCS prior to pyrolysis maintained mesoporosity to temperatures of 1200 degrees C, however, micron-sized SiC powders did not maintain porosity above 800 degrees C. The modal pore size in pellets formed by compressing micron-sized powders with the preceramic polymer was 5 mu m compared to 30 nm when nano-sized powders were used. (C) 2008 Elsevier B.V. All rights reserved.