Copper is a very good heat conductor.
In the Mishkan the outside Mizbeach was made of copper, and had a fire burning on it continuously. (Actually it's a dispute if it had 3 or 4 fires burning on it daily.)
Certain types of Avoda (Temple services) required the Cohanim to step onto the actual Mizbeach.
Every morning they had to do Trumat Hadeshen - take a spoonful of ashes off the Mizbeach.
They frequently removed all the ashes.
They had to prepare new bonfires daily and then light them.
As we know, the Cohanim had to serve barefooted.
How did the Cohanim walk on the copper Mizbeach without getting their feet burnt? We don't find this mentioned as one of the miracles that happened in the Mikdash.