Nanofiber-based aerogels or sponges are made from preformed polymeric nanofibers. They are very porous, ultralight and have a large internal surface as classical aerogels. But their network of interconnected fibers renders them also elastic and mechanically resilient. Moreover, they show a hierarchic architecture with minor primary pores between tangled nanofibers and major cell-like pores. Nanofiber aerogels can be tailored to many applications due to flexibility in the choice of polymer together with the possibility to chemically modify the surface of the fibers. Possible applications include filtration, thermal insulation, support for catalysts, or scaffolds for tissue engineering. Mostly, synthetic polymers such as PAN and PVA have been used as fiber materials or their blends with biopolymers such as pullulan and gelatin.