But its also measurable in its own right surely? We can see its affects for example. Its not a void. But then I did opt for literature over science...

The instruments we use to measure temperature actually measure the presence of heat in some form or another [ex. liquid thermometers use a fluid which increases in volume when heat (or energy) is present rather than when "cold" is present]. In the grand scheme of things this probably doesn't matter much haha, interesting none the less.