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Nanohybrid silica/polymer aerogel monoliths were produced by the soft sol-gel process and dried at ambient pressure. The hybrid alcogels were prepared by a two-step acid/basic catalyzed co-hydrolysis/co-condensation of a silica precursor (tetraethoxysilane) and cross-linked poly(butyl methacrylate-co-butyl acrylate) nanoparticles with core and core-shell morphologies, both containing trimethoxysilyl-functionalized poly(butyl methacrylate) groups. Polymer nanoparticles (PNPs) with average diameters ranging from 32 to 132 nm, in contents from 1 to 9 wt%, were used. The PNPs act as nucleation sites for the silica network, which grows with similar structure to the purely inorganic one, although more hydrophobic and thus stable under atmospheric conditions. The macropore and mesopore morphologies of the nanohybrid materials are significantly modified by the presence of the PNPs. The effects of PNP size and content on the hybrid aerogels properties are not independent: for each PNP dimension, there is a particular content that results in a minimum value of apparent density, maximum porosity and larger mesopore dimensions. This content corresponds to the critical aggregation concentration of the PNPs, which depends on the particles' size. Keywords: Aerogels, Hybrid nanocomposites, Polymer nanoparticles, Silica