Since the properties and degradation reactions of plastics are usually influenced by their formulations and manufacturing processes, this chapter will first discuss those areas. Four plastics have been identified as being more vulnerable to degradation than others in museum collections; cellulose nitrate, cellulose acetate, plasticised PVC and polyurethane foam. The most frequently seen188 Chapter 8 degradation reactions and the possibilities for conserving these plastics will be presented in this chapter.