Why does popcorn pop, and why do some kernels stay unpopped?

Popcorn pops because each kernel contains a specific amount of water, ideally around 14%, trapped inside a tough outer shell called the pericarp^[1][4]. As the kernel heats above 180°C, this water turns into pressurized steam, transforming the internal starch into a hot, gelatinous material^[1][5]. Eventually, the pressure becomes too great for the hull to contain, causing it to rupture and the starch to expand rapidly, flipping the kernel inside out^[1][4].

Kernels fail to pop if their moisture levels are too high or too low, or if the hull is damaged and allows steam to escape prematurely^[2][6].