Boyle's Law

Boyle's gas law complements Charles's gas law. Boyle's law states that when the temperature is held constant, the volume of a fixed mass of gas in a container varies inversely with the pressure.

In other words, as long as the temperature of a gas such as propane doesn't change, the volume of the gas will decrease proportionally to increases in pressure, and vice versa.

As a corollary, think of a bicycle tire or a tank that holds helium to blow up balloons. The higher the pressure, the more air there is in the tire or helium in the tank.