Why do those long, white clouds form behind jets flying high overhead?

Key Takeaways
  1. White paint helps reflect sunlight and heat, keeping the aircraft cooler.
  2. White paint also helps in reducing fuel consumption and maintenance costs.

The clouds that jets form on certain days are called condensation trails or contrails. Some days, the contrails will form thin lines that cross the entire sky. Other days they will be much shorter, and on some days there will be none at all.

A contrail forms because one of the components of jet engine exhaust is water. Jet fuel is made of carbon and hydrogen (see this Question of the Day for details on fuel, and see How Gas Turbine Engines Work for details on jet engines). When jet fuel burns with oxygen, most of the exhaust consists of CO2 (carbon dioxide) and H2O (water). The water is generally an invisible vapor.


When you exhale, your breath contains a great deal of invisible water vapor as well. You may have noticed that on certain days in the winter, your breath will form a cloud of condensation when you exhale. In the summer, however, you don't see your breath. Cold air can hold a lot less moisture than warm air, so in the winter, when the moisture in your breath hits the cold air, the moisture condenses into a visible cloud.

The same thing happens when a jet engine "exhales." If the temperature, winds and humidity in the upper atmosphere are right, long, white contrails form when the moisture in the exhaust condenses.

These links will help you learn more:


Frequently Asked Questions

Are there any disadvantages to painting airplanes white?
While white paint may make it harder to detect ice accumulation on aircraft surfaces during flight, potentially increasing the risk of ice-related hazards and requiring additional precautionary measures during adverse weather conditions.
How do airlines and aircraft manufacturers choose the specific shade or type of white paint for their aircraft?
Airlines and aircraft manufacturers consider factors such as heat reflectivity, durability and ease of maintenance when selecting the shade or type of white paint for their aircraft, often opting for specialized aviation-grade paints formulated to withstand the rigors of flight and provide optimal performance over the aircraft's lifespan.