Batman Bat Signal Heat Changing Coffee Mug - DC Comics Officially Licensed - - Add Hot Water and Batman Comes to the Rescue - Comes in a Fun Gift Box When the mug is cold, the Bat-signal lights up the sky - looks like there's trouble in Gotham City! When the mug is hot, the Caped Crusader appears to save the day! 14 oz. ceramic mug. Comes in a colorful box. Color changing cups are microwave safe, but not dishwasher safe. Hand wash only. Don't soak. Click on "The Unemployed Philosophers Guild" above the product title to see more great gifts. UPG truly has presents of mind.