First things first, you can't make just any type of corn pop.
When you heat the popcorn up, the tiny bit of water inside the kernel changes into steam and expands.
Around 212 degrees [Fahrenheit] the water turns into steam and changes the starch inside each kernel into a superhot gelatinous goop. The kernel continues to heat to about 347 degrees. The pressure inside the grain will reach 135 pounds per square inch before finally bursting the hull open.As it explodes, steam inside the kernel is released. The soft starch inside the popcorn becomes inflated and spills out, cooling immediately and forming into the odd shape we know and love.
But the fun doesn't end there. There are actually two types of popcorn: mushroom and butterfly.
The two types form in slightly different ways.
With mushroom popcorn, the kernel expands evenly. But with butterfly popcorn, the starch inside comes out of wherever the kernel's skin breaks, basically turning it inside out. You can see butterfly popcorn forming in these GIFs: