Sure gold is a thermal insulator. It's not semantics, it's technical terminology what it's at stake.
Heat transfer occurs by convection, radiation or conduction (duh!). Gold is a poor conduction insulator and a very good radiation insulator for infrared wavelengths (the range of almost-100% reflection starts at the infrared while it blocks about half of the visible light, that's why it's used in astronaut helmets: you can see but you're not fried).
It is also very cheap: a space helmet uses only 0.1 grams of gold to block almost all infrared, that's worth about 8 dollars.
If you want to appear to be rich but spend very little money, coat your heat sensitive areas with gold foil (available at many paper vending sites):
It's very efficient on a per weight base, because very thin layers work well, and few materials can produce layers so thin: that's why it is used at the back of F1 seats and on top of some engines.
Even McLaren F1 sports car has it on the engine cover:
It is immune to rust when heated, something that's not true of silver or aluminium, so it keeps its reflectivity. Thermal blankets doesn't last long around exhausts, much less stay pretty, as I can attest by personal experience.
Gold barriers are so light that they are used in many space probes.
It seems like gold foil, but it's not. The method is called
multilayered thermal insulation, probably the most efficient method of thermal insulation by weight. The fundamental idea is that radiation and reflection are balanced: the insulator receives as much thermal energy as it radiates and reflects.
Multi layer thermal insulation at the Large Area Telescope - Goddard: ten layers of very thin Mylar plastic, covered in gold, insulate the probe from almost all the heat. I wonder when we will see it in F1 (or notice it, if it's already used)
