In this study, a novel approach was introduced to reduce the brittle behavior of phenolic aerogels. Hydroxy-terminated polybutadiene (HTPB) resin, a low-molecular weight rubbery material, was used to modify novolac-type phenolic aerogels. The aerogels were prepared by two-step sol-gel polymerization at high temperature/pressure process followed by ambient pressure drying. First, HTPB chains were introduced into the novolac network during the gelation and then, were consolidated in the novolac structure through reaction with toluene diisocyanate (TDI). The resulting aerogels containing different amounts of HTPB (0-50 wt%) exhibited low bulk density in the range of 0.14-0.23 g/cm(3). By increasing the amount of HTPB, the change was observed in microstructure, morphology, and physical properties which corresponded well with mechanical properties and thermal conductivity variations. The measured compression modulus of the aerogels was found to decrease from 96.0 (for pure novolac) to 11.8 MPa with addition of HTPB, indicating some extent of flexibility in the network.