A process for preparing a filter plug for a smoking article, such as a cigarette, includes: (a) freeze-drying a solution of a biopolymer to form a structure; and (b) cutting the structure to a predetermined dimension, to thereby prepare a filter plug for a smoking article. Another process for preparing a filter plug for a smoking article, such as a cigarette, includes: (a) extruding a mixture of a foaming agent and a biopolymer comprising a protein to form a structure; and (b) cutting the structure to a predetermined dimension, to thereby form a filter plug for a smoking article. A cigarette is also disclosed comprising a tobacco rod and a filter attached to the tobacco rod, wherein the filter comprises a filter plug prepared according to the process of the invention and the structure obtained in the extruding has an average pore size ranging from about 0.04 mm to about 0.20 mm.