If the plastic lunch box is made of polypropylene (PP) or polyethylene (PE), it can be heated in a microwave oven. However, long-term high-temperature heating should be avoided.
Each plastic has its heat resistance limit. Among the materials for food use, polypropylene (PP) can withstand 140°C, followed by polyethylene (PE), which can withstand 110°C, while polystyrene ( PS) can only heat up to 90°C.
Commercially available plastic lunch boxes for microwave ovens are mainly made of PP or PE. If the temperature exceeds their heat resistance limit, the plasticizer may be released. Therefore, long-term use of high temperature heating plastic lunch boxes to reheat food should be avoided.