Popcorn is a type of flint corn, but has its own size, shape, starch level and moisture content. It has a hard exterior shell and a soft starchy center. When heated, the natural moisture inside the kernel turns to steam and builds up enough pressure to eventually explode. Due to its nutritional value, it is considered a healthy food. here are two main varieties of popcorn, according to the shape it takes when expanded. One of them is the butterfly, which explodes taking an irregular shape. While the mushroom takes a rounded shape when it explodes at high temperature. Popcorn kernels contain a hard shell that contains a starchy kernel with a moisture content of 14 to 20%, which turns into steam when the kernel is heated.