Constructing model hot air balloons is an activity that captures the imaginations of students, enabling teachers to present required content to minds that are open to receive it. Additionally, there are few activities that lend themselves to integrating so much content across subject areas. In this article, the authors describe how they have successfully used hot air balloons to teach metric measurement, proportions, trigonometric functions, density, convection, data collection and analysis, principles of engineering, and many other concepts and skills. (Contains 2 figures.)