The Moscow Mule is a delicious cocktail that is normally served ice cold in a copper mug. The general consensus among Moscow Mule drinkers is that the copper mug keeps the drink colder than a normal glass would, and my subjective experience seems to confirm this. But this doesn't make sense to me: it seems that the opposite should be true. That is, since copper is an excellent conductor of heat, shouldn't heat from my hand and from the air transfer to the beverage faster than normal, thereby quickly transforming my refreshing cold beverage into a room-temperature, ice-melt-diluted swill? What's going on here?
The copper will heat up the drink more quickly, but it will also cool your hand and lips better than the cold liquid itself. Perhaps cool hands and lips is the feeling drinkers experience and favor. You could do simple experiment - put equal amount of drink and ice into copper and ordinary glass, and find out in which one the ice melts down first.
This is believable. The copper (or any metal) has a certain heat capacity, acting as a "thermal mass".
Ceramic or glass does too, but as heat insulators, only the surface of the material in direct contact with the drink matters. It quickly matches the temperature of the drink, but only a thin layer touching the fluid. Only the little bit of heat in that layer affects the fluid warming it very slightly. Wait long enough of course, it'll all reach room temperature since nothing is a perfect heat insulator, and there's thermal IR and so forth.
Compare to a heavy copper mug. If it starts at room temperature, all the warmth in the copper will flow to the fluid, warming the fluid while cooling the mug until they reach somewhere in the middle. Clearly this is not what is claimed! But the mug feels cooler in one's hand, which maybe fools some humans.
But what if the copper mug is initially chilled to around the same temperature as the drink? Then any warming effects, from one's hand, from thermal IR of the environment, will have to warm up both the fluid (same amount as contemplated in the ceramic/glass mug) and all of the copper. Any heat added to the copper will spread, since it's a conductor. It will take longer for the combined drink + mug mass to reach room temperature. OTOH, there is the warmth of one's hand on the mug - is the handle part of the same copper structure, or a different material?