Another natural material (e.g. another wood, wax, biodegradable material)Glues, resins, or other substances to promote adhesionSubstances to prevent adhesionA combination of two or more of the above It is further envisioned that if the stopper has multiple portions (e.g. such as shown in the embodiment of FIG. 2B), each particular portion may be comprised of one or more materials.Materials and/or