the impregnation of a foam rubber , or similar polymeric material , insole with an effective antibacterial and antifungal agent along with a deodorant provides a simple , clean source of active ingredients for curative and prophylactic treatment of infections of the feet and reduces odors during the course of the treatment . the agent of choice in such a product must be stable to the conditions of use and be sufficiently non - volatile to be retained in the insole over a period of days or weeks .