The tea cozie apparently came about when a woman, tired of her husband complaining of cold tea, plopped his hat down over the pot until he was ready to drink it. She found that it worked, and soon, there were specific little caps to put over teapots, the tea cozies we know today.
Everything Ok! on Etsy.com took the idea of the cozie a step further, and created: the tea mug cozie.
I have a set of four, which were custom-made for me in the color scheme that I wanted, at no additional charge, and they were delivered in a timely fashion as well. I love them, and they really do keep my tea warm. When not in use as warmers, they keep the dust out of my mugs, and make a lovely conversation piece as I keep them out on display!