Heat-activated mugs are special drinkware that change color or reveal hidden designs when filled with hot liquids. These mugs typically use thermochromic materials, which react to temperature changes. When you pour in a hot beverage, the heat causes the mug's surface to alter its appearance, creating a fun and interactive experience. These mugs are popular for personal use and as gifts, often featuring themes from movies, TV shows, or video games. They are usually made from ceramic or stainless steel and are designed to be both functional and visually appealing, making them a unique addition to any kitchen.