Even though paraffin interactions with plastics are known by industry, plastics are commonly proposed as container materials for encapsulating phase change materials (PCM) in many applications. In the literature, there are very few experimental studies of organic PCM migration in plastics and its effects on plastic properties. These interactions are a case study of environmental stress cracking, which is considered one of the most common causes of plastic failure. The aim of this work is an experimental study of interactions of some PCM typically used for thermal energy storage, and some plastic materials currently used as encapsulating materials. With the materials tested in this work, it can be concluded that, for encapsulating organic PCM, low-density polyethylene and polypropylene showed worse behaviour than high-density polyethylene. Copyright (C) 2010 John Wiley & Sons, Ltd.