Why popcorn is a good insulator?

Answer 1

Theoretically, popcorn would be a good insulator due to its composition of mostly air and corn, both of which are good insulators.

Popcorn is better than good, because it is an NIC foam. NIC stands for non-intercellular, which means that the thousands of gas-filled cells of which it is made do not communicate with each other, or with the outside world. Each cell is a sealed space. In fact this is why corn pops when heated; the steam produced inside each cell can't escape, so it inflates the cell, which inflates the corn. One of the best artificial insulators is foam polystyrene, also NIC and about as lightweight as popcorn.

For contrast a household sponge is intercellular. Great for soaking up water, but useless as an insulator.

Note. In this answer insulator refers only to thermal insulation, not electrical.