1. [SET OF 4 & SAFETY SILICONE MATERIAL]: The 4 pack collapsible food storage containers contains 2 square (350ml and 500ml) and 2 round boxes(350ml and 500ml) which satisfy variuos needs of food storage. Moreover, each container is made of superior BPA free food-grade silicone which is soft, unbreakable and non-toxic. 2. [AIRTIGHT STORAGE AND SAVE SPACE]: The snap buckles and Vent Valve create an airtight space, in order to preventing dust and maintaining the fresh of food for a long time. In addition, these collapsible food storage containers are also collapsible, which is easy storage and can be folded for saving space approximately 50%. 3. [MICROWAVE & FREEZER & DISHWASHER SAFE]: It's dishwasher, freezer and microwave safe. The temperature tolerance of the leftover container is approximately -4°F~428°F/-20°C~220°C. TIPS: It must PULL UP the AIR VENT VALVE on the lid or REMOVE THE PLUG before HEATING!!! 4. [MUlTIFUNCTIONAL]: The 4 pack collapsible meals Prep containers include square and round containers with small (350ml) and middle(500ml) size, which adapt to various condition. For instance, storing cereal, fruits, vegetables and leftovers in the fridge. Furthermore, it also can be used as lunch box for office workers. Moreover, if you go outside for travleing or camping, it help to carry the food conveniently XD.