Japan manages materials in contact with food using a "positive list" system, which is a method that lists all chemicals recognized and permitted for use in food contact applications. The positive list specifically applies to synthetic resins but does not cover materials other than synthetic resins. It is intended for substances that are released from utensils, containers, and packaging and transfer to food, affecting it; substances used for anti-static or anti-fog purposes that are applied to the surfaces of raw materials such as utensils, containers, and packaging; substances produced by chemical changes in the raw materials; and substances that are not expected to remain in the final product, such as catalysts and additives that support polymerization reactions. In the Japanese Positive List for Food Contact Materials - Base Materials, "base materials" refer to polymers that are solid at room temperature and pressure and have a molecular weight of over 1000. The list categorizes materials into 21 types of polymers and 5 material categories. Appendices 1 to 21 provide a reference list of monomers and combinations for base materials. Each base polymer must consist of at least one required monomer listed in the corresponding appendix, and may include a combination of optional substances and/or chemical treatments as needed.