Recently phenolic foams have been spotlighted because of their excellent flame resistance, high thermal stability over a broad temperature range and low generation of toxic gases during combustion. However, phenolic foams have inferior mechanical strength and high thermal conductivity compared with other polymer foams, and it is difficult to control the cell morphology by forming different sizes of pores during the foaming and curing process because phenolic resins contain various solvents. In this work, the nanoparticles such as multi-wall carbon nanotubes (MWCNTs) and graphene-reinforced phenolic foams were fabricated to control the cell morphology. To improve the thermal and mechanical properties of the phenolic foam, the proper foaming point of each particle-reinforced phenolic foam was investigated by cure monitoring using a dielectric sensor. From the experimental results, the effects of viscosity and the dispersion of particles on the cell morphology was introduced, and the optimal weight fraction of each particle was found based on the cell morphology and the thermal and mechanical properties of the phenolic foams. (C) 2014 Elsevier Ltd. All rights reserved.