PP marked polypropylene containers. PP containers are a microwavable version of food containers. PP has a heat tolerance of -20 degrees Celsius to +110 degrees Celsius. For this reason they can be used for a much wider range of food packaging. They are equally suitable for frozen goods as for hot food. They are practical because they are disposable/disposable, so you don't have to worry about washing them. They can be stacked on top of each other.