Natural sponges are a unique class of complex materials and represent the simplest form of multi-cellular creatures.For example,a sponge with a density of 15 mg/cm3 had a fiber interconnected structure with a fiber diameter of 20 μm.Electrospinning is known as an excellent method to prepare fibers with fiber diameters in the submicrometer range.[1] Here we report on ultra-light 3D polymer sponges,which were prepared by freeze-drying of dispersions of short electrospun nanofibers(Figure 1).[2] With the use of dioxane as solvent we discovered the formation of a complex hierarchical network of pores.As a consequence open cell soft polymer sponges with extremely low densities were obtained with high mechanical integrity.