My wife recently got me a new travel coffee mug and it’s the best one I have ever had as far as keeping the coffee really really hot for a long time. It is very thin walled and I just don’t understand how the heat does not transfer to the outside surface of the cup.
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So there’s two ways the heat from the coffee can reach the outside.
Convection. The whole warm air rises kinda thing.
And conduction which is what you’re thinking of for why shouldn’t it pass through.
The mug is made up of a two thin walled steel tubes with a gap in between. If this gap is a vacuum then there isn’t any particles of air to transfer heat via convection.
The thin wall means only a small amount of heat can travel in the steel and has to travel a really long way again reducing the conduction. Finally steel is a much worse conductor of heat than aluminium.
Finally it could transfer heat through radiation but again the vacuum will prevent this.
It’s this thin walled can set up which makes for an amazing thermal barrier at keeping something hot, hot. Or cold cold without needing much energy.
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