Energy Star is a program run by the US Environmental Protection Agency that certifies different types of products as energy-efficient according to different metrics specific to each type of product. For refrigerators, Energy Star certified models are on average 9% more efficient than the minimum requirement for efficiency set by the Department of Energy. According to the Energy Star website, "certified refrigerators offer high performance features such as high-efficiency compressors that create less heat and use less energy, improved insulation that helps food stay cold, and temperature and defrost mechanisms that help the refrigerator operate more efficiently." Energy Star appliances can also save you money over time.