This series of container’s does it all- it can be stored in both the refrigerator and the freezer, and can be microwaved with the lid on once the top flap (steam-releasing vent) has been opened. The main body of the container and top of the lid is made out of a transparent, light weight, high heat resistant soft polypropylene. The edges of the lid are made out of thermoplastic elastomer, which has been fused to the main body of the lid to provide excellent sealing capabilities, while remaining easy to open and shut as well as to wash clean. Just by opening the flap in the lid, steam is released during heating, allowing the contents to cook to perfection. Strong against contact with alcohol, vinegar and oil. Dishwasher safe, for sterilization purposes. The steam vent cleared a durability test, requiring it to be opened and closed over 20,000 times. The handle on the container allows you to hold it with bare hands right after being heated. This all in one container is a must have item!