A detailed transport model is used to predict the effects of the widely variable physical properties (density, thermal conductivity, permeability to gas flow, specific heat capacity) of the feedstock on the convective-radiant pyrolysis of cellulosic fuels. For conversion in a thermally thick regime (intra-particle heat transfer control), it is found that variations in the physical properties mainly affect the activity of secondary reactions of tar vapours and the conversion time. The highest sensitivity is associated with the biomass density and the char thermal conductivity. Physical properties weakly affect only the conversion time in the thermally thin regime (external heat transfer control). Applications of these findings in reactor design and operation are discussed.