Constructed of nonporous glass that never absorbs stains or odors, the transparent dishes can be easily monitored while baking, and their contents can be quickly identified when stacked in the refrigerator or freezer. Furthermore, they nest together for space-saving storage when not in use. Best of all, each dish comes equipped with two matching lids: a BPA-free plastic lid that works well for sealing shelf-stable, refrigerated, or frozen contents and a silicone-rimmed, self-venting glass lid designed especially for microwave and oven use. The glass bowls and lids can be safely placed in the microwave or pre-heated oven, and all pieces offer refrigerator-, freezer-, and dishwasher-safe use (plastic lids should be placed on the top rack). Made in the USA, the 12-piece set carries a two-year limited warranty.