Each container in this 56-piece set is made from BPA-free polypropylene for peace of mind. The super-clarified bases make it easy to see the contents and the square shape allows for optimal space utilization. They come in graduated sizes that nest for compact storage. The unique lids also snap to each other and to the bases for stacking and storage. Best of all, they are microwave-, dishwasher- and freezer-safe for a range of kitchen applications.