No, space station

Airplane!

Idiot. You obviously have no idea about the logistics of launching a bath into space. You'd need to send a bucket on a rocket (aero dynamic).

Put the ISS into the bucket, fill with water, then squeeze the ISS and look for bubbles.

It's not cold physically, it's cold emotionally.

My brain just imploded from that realisation and it troubles me.

I can intellectually reconcile what you said, but my reptilian brain cannot comprehend the phenomenon for whatever reason.

I instinctively don't believe that the radiation only is how heat is transferred in the vacuum even though I know that this the case. We always have had 3 (convection, conduction and radiation), and that stumps me.

If you really play with definitions you can equate cold to things that are thermal insulators and hot to things that are conductors. By that (very stretched) definition a vacuum is cold. Perfectly cold.

The stretching: Even if something is like a thousand degrees but it's a near perfect thermal insulator, it won't feel that hot when you touch it.

Heat transfer by radiation complicates things. We lose the majority of our heat that way, and we'd lose a lot more if every cubic inch of the spaces we inhabit weren't flooded with thermal radiation from the objects that surround us.

You can absolutely judge the temperature of a volume, vacuum or not, by its radiation content at any given moment.

The only reason to use gases for this on earth is because liquids are too heavy to be sucked towards to small leaks. In space, isn't there a case to be made to use some small light solids? Not styrofoam because theyre staticky. But if you found something of equivalent density that would float towards the leaks, but didn't pick up static and could easily be cleaned out of the air filters...it would be useful for this.