Inside a vacuum chamber, marshmallows and balloons expand significantly as the air inside them pushes outward against zero external pressure.

This phenomenon is a direct demonstration of Boyle's Law, which was first published by Robert Boyle in 1662. The law states that the pressure and volume of a gas have an inverse relationship when temperature is held constant. In a standard environment at sea level, the Earth's atmosphere exerts a pressure of approximately 101.3 kilopascals on all objects.A marshmallow is essentially a foam consisting of roughly 50 percent air by volume, trapped within a matrix of sugar and gelatin. When a vacuum pump removes the air from the chamber, the external pressure drops toward zero. The internal pressure of the air bubbles remains high, forcing the elastic sugar walls to stretch and expand until the internal and external pressures equalize.Balloons behave similarly because the air molecules inside collide with the rubber walls more frequently than the thinning air outside. However, marshmallows undergo a permanent change. As the marshmallow expands, the delicate sugar membranes eventually rupture, allowing the internal air to escape into the vacuum chamber.When the vacuum is released and atmospheric pressure returns, there is no longer enough air inside the marshmallow to support its structure. This causes the marshmallow to collapse into a shriveled, dense, and toughened version of its original self. This experiment is a staple in physics education to illustrate the physical properties of gases and the effects of atmospheric weight.