According to the Tupperware Brands Corporation, only Tupperware products specifically designed for microwave reheating or cooking should be used in the microwave. As of 2014, Tupperware's microwave-safe product lines include the TupperWave Stack Cooker, Rock 'N Serve, Vent ’N Serve and CrystalWave.Know More
In 2008, the company began marking Tupperware products with internationally accepted Material Identification Codes for recycling purposes and usage symbols that denote whether or not a product is safe for use in the oven, microwave, freezer or dishwasher. Typically, these markings are found on the bottom of the product. Any Tupperware item that is not marked with the microwave-safe symbol (a square with five wavy lines) is not safe to use in microwave ovens.