The feeling of hot or cold is actually just the feeling of heat energy entering/leaving your skin.

The basics: if something is cold, energy is moving from your hand into the cold thing. If something is hot, energy is moving into your hand from the hot thing.

If it cannot transfer energy at all, then it doesn’t feel hot or cold. Like when you take a shower at the perfect temperature where the water temp matches your skin exactly, and it doesn’t feel like anything. Or a very warm pool.

Your hand would overheat a little bit eventually because your body creates internal energy through being alive, which it radiates away through your skin to the surrounding air to maintain equilibrium. If your hand lost that ability, it would get a bit warmer internally. But your blood would maintain approximate temperature equilibrium, so it wouldn’t be too bad.

If you were in a pool of the stuff, you’d eventually cook yourself.

Source: got a physics degree a bunch of years ago and kinda remember some things. But I’m not 100% confident of any of this