I use a titanium cup and then use a "cozy" around it and have cut two rounds for top and bottom from an old foam sleeping pad. My current cozy is just the top of an old wool sock. You loose a lot of heat from the top, so even with an insulated mug you need to cover the top.

This way I have insulation for slow drinking and can also set the cup on the stove to boil a small amount of water.