Plastic boxes labeled pp5 can be used, as long as there is no metal component (metal edges), but it is recommended that it is best not to use, you can use your home ceramic bowls to steam the eggs, steaming egg custard with a ceramic bowl can be. Ceramic ones are more heat resistant than plastic ones. I just often steam egg custard, cover a pp5 plastic lid, with the usual heating rice microwave function can be, a few minutes on the good.