Gases that are lighter than air include water vapor, methane, hot air, hydrogen, neon, nitrogen, ammonia and helium. These gases have a lower density than air, which causes them to rise and float in the atmosphere.
Many lighter-than-air gases provide lifting power for airborne objects. Recreational ballooning uses hot air, while ammonia often powers weather balloons. Party balloons are commonly filled with Helium. Hydrogen possesses significant lifting power, but is highly explosive. Methane, the primary component in natural gas, makes a good substitute for Helium and Hydrogen because it does not leak through balloons as quickly as the other two gases.