This shows that water is a bad conductor of heat energy. Heat has not conducted easily through the trapped air to position B. This shows that trapped air is a poor conductor (or good insulator).

If you can’t answer the riddle, don’t feel bad. Metal conductors usually conduct electricity and heat. Usually, that’s true, but researchers at the Department of Energy’s Lawrence Berkeley ...

There are better heat conductors but they aren't practical materials for producing computer heatsinks: silver exceeds copper's thermal conductivity at 429W/mK (hence Arctic Silver thermal paste ...