Relatively speaking there are 2 types of popcorn kernels: Butterfly style and Mushroom style. The difference between the two is the obvious shape of the popped kernel, Simply, Butterfly has wings and Mushroom pops into a ball shape.
But it doesn't stop there.
There are a lot of different colours and sizes of Popcorn Kernels. The biggest difference is the appearance in colour before and after they pop. Yellow and White kernels are what you would normally find on the grocery store shelves. When they pop, they pop into a Butterfly shape. All popcorn is white on the inside, but will have different colours on the outside. Most theatres use a yellow coloured kernel. A White Kernel will be really white when popped.
This has always been a big complaint. When it comes to eating popcorn, a lot of people are bothered by the hulls. They get stuck in their teeth. In general, the white popcorn is better for that group. The hull on it is smaller. All popcorn kernels have Hulls. Some white kernels are labelled as hulless. Not true. This only means that when the kernels pop, the hulls explode enough for you to not detect them when eating them. The mushroom popcorn however, needs the thick hull to hold in all the moisture so the steam can build up to create the explosive pop and large "mushroom" for which the popcorn is named. Because the hulls are so thick, they don't shatter when the kernel pops so you will notice a lot more of them after popping. Mushroom popcorn is almost always used in Candy Coated popcorn because it gets covered and is less noticeable.
When the popcorn has finished popping, sometimes unpopped kernels remain. Known in the popcorn industry as "old maids", these kernels fail to pop because they do not have enough moisture to create enough steam for an explosion.
The first automatic popcorn machine was introduced at the 1893 World's Fair in Chicago by Charles Cretors.