A process for preparing a cellulosic sponge includes the steps of treating an aqueous suspension of cellulose fibers with periodate; adjusting the pH of the resulting dialdehyde cellulose fibers suspension to a value between 2.5 to 5.5; freezing the suspension obtained and thawing the three dimensional structure to render the cellulosic sponge. The process may further include a step of drying to render a cellulosic foam. Both the new sponge and the new foam may also be further chemically modified obtaining a broad variety of derivatives with tailored properties which are useful in many different applications.