I think coffee tastes much better out of my older (vintage) glass vacuum thermos than it does out my new stainless steel one.
The coffee also stays hot overnight in the glass type.
What do you use?
Kitchenaide single cup, 16 oz, coffeemaker with an insulated 16 oz cup. Good coffee helps
I think glass is a better insulator but more fragile. Steel is a conductor and radiates the heat to the air inside. I know that I prefer glass in my thermos but I'm a klutz so I tend to break things often that are mine (not customers thankfully *Knocks on wood*). I think that if you want things hotter and longer, glass is the way to go. For the taste however, I'm not sure. I think that maybe after all the years of coffee in your thermos, you've added that famous "aged" taste. It's infused with coffee of old.