Popcorn is a variety of corn seed that pops when heated. The seed is made of a relatively stronger cover surrounding a hard body of starch mixed with a little bit of water. When the seed is heated, the water turns into steam.
But steam needs almost two thousand times more space than liquid water, so the pressure inside the seed rises violently, as in a pressure cooker, until the cover breaks open. At this stage, the starch inside the seed has become softer because of the high temperature and pressure. When the seed pops open, the starch comes out with the steam and then turns into a crispy white foam while cooling down. All of this just because some water was heated past its boiling point, where it became pressurised steam!
Picture Credit : Google
