While checking out the local hardware store wire section, I came across thermostat wire priced significantly lower than other types. I have been trying to determine the reason but details online are skimpy.
I want to play with different HF style of antennas at low cost for some SOTA QRP and wondered if this might fit the bill without breaking the bank?
Thermostat wire will be cheaper than the wire near it on home-improvement shelves because it is smaller — it does not carry high current or high voltage in the intended application, so it does not need to be thick or have strong insulation.
This, in itself, is fine for HF antennas — except in high-power applications, the current is not a problem, and the voltage is better addressed by distance than by insulation.
However, it is probably solid wire. Solid wire is not a good choice for portable wire antennas because repeated bending will fatigue and break the copper. (It's okay to use solid wire for a self-supporting rigid antenna such as is found in VHF and higher frequencies, though copper is a bit soft for that application.)
You should look for stranded wire for building antennas if you want them to last.
I agree with @KevinReidAG6YO that it is generally better to use stranded wire.
But given the itinerant nature of a SOTA activation and the apparent low cost of the wire, I would say go ahead and use it! Try not to flex it in a tight bend too often or it will break. When you are done with an activation, roll it into a loop of six or so inches in diameter to minimize the work hardening of the wire.
When it does finally fatigue, simply pull out another length and start again.
