All popcorn contain a small amount of water. When the popcorn gets heated the water inside the popcorn kernel turns to steam. The steam then starts to pressure the kernel shell and soon bursts making the kernel inside out, and the soft stuff inside the kernel puffs.
Popcorn pops period because in the kernel (ker-nelle) or nut, there is water.So when the heat or fire touches the water inside the kernel,the water creates pressure and the kernel turns inside out which creates what we Americans now call popcorn.
Popcorn "pops" when the internal temperature of the kernel reaches a certain level. Anything that raises the temperature of the kernel can potential cause it to pop. Lookup "Popcorn air popper" for an oil-free alternative to cooking popcorn.