The Lid creates an airtight, watertight seal for reheating and storing. It can also be used while serving food, to keep your dishes hot or cold for longer. Each lid is microwave, dishwasher and heat safe up to 428 degrees Fahrenheit. Perfect for reheating and storing leftovers. It's creates a tight seal on all smooth rims, be it stainless steel, glass, plastic, or melamine.