This was a shocking revelation to me.

I always assumed there was some magic technology in microwave popcorn bags.

nope. The bag prevents the popcorn from scattering, and any kind of bag or container will work

"Microwave Susceptor". Its a super thin layer of aluminum or graphite that absorbs microwaves and gets really hot. Its in the bottom layer of the bag and the reason for "this side up".

Interesting how I can get almost every single kernel to pop without burning in a plain paper bag.

Wow, I assumed similarly - that there's something in the bag that helps the air inside heat up. I guess maybe moisture in the corns is enough. I learned something new and useful today, thanks!

Guess how early (70s) microwave cookbooks told you how to make popcorn, before Orville Redinbacher got involved. Yet my wife, same age I am and read the same cookbooks, buys pre-packaged unflavored microwave popcorn from the store. </shrug>