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.