The ProKeeper+ 4-piece airtight storage set by Progressive features a superior structure and a silicone seal that ensures airtight storage. Its stainless steel clasp also ensures the longevity of the ingredients. The four containers are designed to maintain the freshness of their contents for long periods. In addition, each container has measuring markings to provide a clear view of its internal contents. The set includes one large 2.5 litre container, two medium 1.5 liter containers, and a small 1/2 gallon container, all with stainless steel hinges that open for easy filling and measurement, an easy grip lock to secure the lid.