Featuring a unique 4-hinge locking system for freshness that lasts longer, Lock n Lock Purely Better storage containers are constructed from borosilicate glass, which can withstand both high heat and sudden cooling but is 10 percent lighter than tempered glass for easy, on-the-go use. The airtight and leak-proof lids have been durability tested to last up to 3 million uses, and feature an innovative steam vent to prevent pressure build-up when foods are heating or reheating. Plus, Lock n Lock Purely Better glass containers are microwave, freezer, oven, and dishwasher safe. Lock n Lock Purely Better containers are also stain and odor resistant, easy to clean, and come with a Lifetime Limited Warranty for healthy, happy, no-worries food storage.