What Makes a Balloon Inflate?

Theory

• Elastic rubber balloons rely on a delicate balance between their own elasticity and the differential pressure relationship between the inside and outside the balloon, with the interior being at a slightly higher pressure. As air is forced into a latex balloon either by exhalation or from a pump or tank, the pressure inside increases slightly as the volume of space inside the balloon increases proportionately to the increase of the number of molecules of air inside the balloon less the volume detriment due to the pressure increase. When the force from pressure inside the balloon pushing the walls of the balloon outward equals the combined forces of the outside or atmospheric pressure plus the force component from the continuously stretching latex rubber, the forces are balanced and the balloon stays the same relative size, until natural leakage through the knot and through the pores of the rubber decreases pressure.

Air Versus Helium

• Filling a balloon with air makes the whole balloon slightly heavier than the air around it because the interior air is slightly denser, and the weight of the latex rubber itself is added to that difference. Filling a balloon with helium is a different story however, since the helium gas occupying the inside of the balloon is so much lighter than air by virtue of its far lower molecular weight. So the difference yields net buoyancy while the balloon maintains a relatively high volume, and the balloon will rise into the air as opposed to the air-filled balloon that will float to the ground.

Latex Versus Metalized Plastic

• Metalized plastic film has grown in popularity in recent years because of the infinite number of variations in color and design that can be implemented, not to mention the flashier shiny appearance. This material has virtually no elasticity, however, so once the volume and shape determined by the fixed geometry of the design is reached, adding more air or gas will only increase the internal pressure and firmness of the balloon, but not volume or size. Minus the elasticity factor, all of the above principles apply.

Weather Balloons

• High-altitude balloons are released from the ground with scarcely the volume they need to rise. As they go higher, they get dramatically larger as atmospheric pressure drops around them until they disintegrate, abruptly ending the mission.

Catheter Balloons

• Catheter balloons are inserted into coronary arteries to open vessels clogged by layers of plaque.