Insulator

Space is actually a good insulator because it is difficult to transfer heat to nothing.

Source: tatoeba (5350184)

It's a great insulator, keeping hot foods hot and cold foods cold.

Source: tatoeba (11280147)

What's surprising is that reducing certain materials from the macro to the nano scale radically changes some of their properties. For example, gold becomes a liquid at room temperatures, aluminum becomes combustible, and silicon turns into a conductor instead of an insulator. So these very small materials behave in ways that are not yet completely understood, and just the fact that they are unimaginably small creates a lot of the controversy. People fear that smaller nanotech particles in the environment might be accidentally absorbed by the human body, that invisible surveillance devices could watch our every move, or that microscopic new weapons would threaten our security in unforeseen ways.

Source: tatoeba (12250679)

To isolate electrical wires from the pylons supporting them, one often uses glass insulators.

Source: wiktionary