The most commonly used take-out box on the market is No.5 plastic polypropylene (PP). In addition, the logo of polypropylene (PP) can also be seen on the outer packaging of rice balls or sandwiches in convenience stores. The outstanding feature of PP plastic is its good heat resistance, and its melting point is about 170 degrees Celsius. It can be used in the environment of 100 degrees Celsius, and there is not much problem as a container or outer packaging for heating food.

The take-out box made of PP is safe and heat-resistant, but different ingredients and heating time must be well grasped. There was an experiment in which the media bought four different brands of PP lunch boxes. After the braised pork was put into PP lunch box, it was heated in microwave oven for about 12 minutes, and all four lunch boxes were melted and deformed to varying degrees.

The deformation of PP lunch box is related to the food inside. Because braised pork contains a lot of oil, and the boiling point of edible oil is higher than 250 degrees Celsius, which exceeds the high temperature resistance limit of PP material, so the lunch box will melt.