Homebrew heaters using resistors?
First time poster! :)
I've been reading up on some projects on this site centered around small homebrew heaters. One I came across I want to adapt is using two resistors and usb port power to make a small coffee mug heater.
I'm kind of a novice at electronics, but I'd like to know how to design such a heater with safety and functionality in mind. I also want to control this heater via arduino if I can get a prototype together. Some questions I have:
Where to get and what kind of resistors for heaters?
How do I figure out what resistors to use based on power. e.g. 12v or USB power?
What's a good thing to "encase" the resistors with that will withstand heat? I have thought about using radiator repair epoxy.
Thanks for any help!