The lid and main body of this storage container is made out of polypropylene. A flap is built in the? lid, allowing you to microwave it with the lid on. Steam escapes through the flap, preventing contents from becoming watery and protecting the flavor. Even if the contents splatter within the container during cooking, the microwave will not be dirtied. High transparency allows you to see the contents clearly, and measurements are printed on the side. Strong against contact with vinegar, alcohol, and oil-based foods. Any type of ingredient can be stored in this container. Easy to wash and easy to stack. Easy to store without taking up unnecessary space in your cabinets. Handle allows you to hold the container with bare hands right after heating. Cost-effective 4 piece series of 400 ml capacity square-type containers.