We discuss the results of atomistic molecular dynamics simulations of both unfilled and nanosilica filled silicone-urea copolymers consisting of soft poly (dimethylsiloxane) and hard bis(4-isocyanatocyclohexyl) methane segments (SS and HS, respectively). The simulations show that due to hydrogen bonding between the urea groups, the polymer segments tend to microphase separate into soft and hard domains. Using an approach based on the numerical analysis of spatially coarse-grained density fields calculated from time-averaged scattering amplitudes, we observe the formation of an irregular bicontinuous structure that can be pictured as an intertwisted sponge-like network where two effectively infinite HS-rich and SS-rich domains are present simultaneously. The HS-rich regions act as physical (reversible) crosslinks, functionally similar to those in chemically crosslinked elastomers, and at the same time as a pseudo-reinforcing filler of the rubbery soft segment matrix. Thus, the phase segregated copolymer itself can be regarded as a spontaneously occurring nanocomposite with hard inclusions embedded in a soft (elastically compliant) phase. The incorporation of silica nanoparticles results in slight improvement of the thermophysical and mechanical properties of the copolymer. The nanoparticles are mainly located in the amorphous phase, in which the soft segments dominate, and do not show a tendency to aggregate. (C) 2018 Elsevier Ltd. All rights reserved.