Carbon-phenolic ablative materials provide efficient thermal protection to space vehicles during their hypersonic atmospheric entry, where huge heat fluxes and mechanical stresses are generated. They have been successfully used in many missions including Mars 2020 and MRS Laboratory 2012. Management of the elevated thermal loads is achieved by low density ablative shields through endothermic pyrolysis reactions of the polymer matrix and consequent outflow of hot gasses. Enhancement in structural resistance is obtained by the infiltration of the resin in a carbon fiber felt reinforcement prior to polymerization. The microstructure and distribution of the resin within the carbon felt can greatly influence the performance of the materials, which can be improved when the phenolic matrix is nanostructured with open and interconnected porosities. The introduction of polymeric additives can modify the dimension and distribution of both the microstructure, characterized by the generation of nano-domains, and pores through the formation of chemical bonds with the phenolic resin. In the present work, different polymeric additives have been employed to modify the morphology of the resin and its distribution within the carbon felt reinforcement. The synthesized materials have been compared to non-nanostructured carbon-phenolic ablators with comparable densities of about 0,30 g/cm3. The microstructure of the obtained composites was characterized in terms of resin morphology and distribution through SEM analysis. The specific surface area and the distribution of pore dimensions were investigated. Improvements in compressive strength were assessed for both virgin and charred ablators. Thermal insulation and ablation resistance were evaluated using the standard oxyacetylene flame exposure test. Therefore, different polymeric additives have been employed to modify the structure and distribution of the phenolic matrix within the carbon fibers reinforcement in order to obtain a nanostructured matrix with open and interconnected porosities thus enhancing carbon-phenolic ablators performances.