Why is propane preferred over butane for fuel in hot air balloons?

Propane is preferred over butane for fuel in hot air balloons largely due to its lower boiling point. This characteristic allows propane to remain in a gaseous state at temperatures that butane might not, making it more efficient for use in the variable temperatures experienced at altitude. When a hot air balloon ascends, the ambient temperature drops, and propane can continue to vaporize effectively, providing a consistent and reliable fuel source for the burner system.

In contrast, butane can struggle to vaporize in colder conditions, which would hinder the performance of the hot air balloon. The ability of propane to function reliably despite temperature fluctuations is crucial for safety and operational effectiveness, making it the preferred fuel choice in the hot air balloon industry.