Common parlance (and a bit of onomatopoeia…) leads us to say that popcorn “pops” when the starch inside the heated kernels changes, water expands, pressure builds … and we hear the sudden “pop”! But a more-scientific take is that the kernels explode, transforming into those beloved, puffy morsels—40–50 times their original size—at just the right time, under just the right conditions.