Metal and enamel products cannot be used for cooking utensils in microwave ovens, because metal can reflect microwaves. It not only causes the heating efficiency of microwave oven to decrease and the heating uniformity to be poor, but also makes the microwave contact with metal to generate sparks, which is dangerous. Plastic products can only be heated by microwave if they are marked with the words "Suitable for microwave oven". Because of the particularity of molecular structure of melamine plastic, unlabeled plastic products are easy to decompose toxic substances, so melamine tableware is not suitable for microwave ovens. Therefore, only pure ceramics (metal-free) and plastic plates marked with microwave can be put into the microwave oven for baking.