A total of six flags have been planted on the Moon – one for each U.S. Apollo landing. Unfortunately, Apollo 11's flag was too close to the landing module and was knocked over by the exhaust when the module launched again. More recently, higher-resolution images from the Lunar Reconnaissance Orbiter show that the other five remain standing. The flags were made of ordinary nylon, so they have long since been bleached by the Sun's UV radiation.

Source: Royal Museums Greenwich