As the kernel heats up, the water expands, building pressure against the hard starch surface. Eventually, this outer layer gives way, causing the popcorn to explode. As it explodes, the soft starch inside the popcorn becomes inflated and bursts, turning the kernel inside out.

Why is my popcorn popping?

The“popability” of popcorn kernels depends on the kernel's water content. When a kernel heats up, the water inside of it releases steam, which puts pressure on the kernel's shell — until it explodes. ... If a hull structure is imperfect, water is able to escape through leaks and the kernel will remain un-popped.

Why do some popcorn kernels not pop?

Popcorn kernels will not pop if they contain too little or too much water moisture inside the kernel. The popcorn kernels which do pop have 14-15% moisture in the hull and anything less or more will cause the popcorn kernel to not explode. You can test the moisture of your popcorn by using your fingernail.