Angel hair or ice wool is a type of ice crystal that forms in the atmosphere and falls from the sky in thin, wispy strands. It is related to the meteorological phenomena of hair ice and frost flowers. It is made of ice crystals that are arranged in a hexagonal shape and are so thin that they appear almost transparent. Angel hair is often seen during cold, clear nights when the temperature is below freezing and the air is humid. It usually forms when there is a lot of moisture in the atmosphere, such as after a snowstorm or during a cold front. The ice crystals form when water vapor in the air condenses and freezes onto airborne particles, such as dust and pollen. The ice crystals then grow and attach to other ice crystals, creating the long, thin strands of angel hair.

Angel hair is a relatively rare phenomenon, but it can be seen in many parts of the world. It is most common in cold climates, such as Canada, Alaska, and Siberia, but it has also been seen in warmer climates, such as Florida and California. Angel hair is usually seen in the early morning hours, when the temperature is coldest. It can also be seen during the day, but it is more difficult to see because the sun's rays can melt the ice crystals.