We report on the preparation of hybrid organic-inorganic porous materials derived from polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) via a single-step molding process. The monolithic, large surface area materials are studied with a particular focus on morphology and porous properties. Radical vinyl polymerization of the nanometer-sized POSS building blocks is therefore utilized via a thermally-initiated route and in porogenic diluents such as tetrahydrofuran and polyethylene glycols of varying composition. Careful choice of these porogenic solvents and proper choice of initiator concentration leads to highly porous monolithic building entities which show a rigid, 3D-adhered, porous structure macroscopically adapting the shape of a given mold. The described materials reflect BET surface areas of 700 m2g-1 or more and maximum tunable mesopore volumes of up to 2 cm3/g. Experimental investigations demonstrate the option to tailor nanoporosity and macroporosity in the single step free-radical polymerization process. While studies on the influence of the used porogenic solvents reveal tuneability of pore sizes due to the unique pore formation process, tailored existence of residual vinyl groups allows facile post-polymerization modification of the highly porous, large surface area hybrid materials exploited via thiol-ene 'click' chemistry. Our developed, simply realizable preparation process explores a new route to derive porous organic-inorganic hybrid adsorbents for a wide variety of applications such as extraction, separation science, and catalysis.