In reply to G0IBE:
Short answer; almost anything.
First dipole I ever made was an 80m trap dipole from hard drawn copper wire and it is still up. It has been cut through twice by a neighbour trimming trees and soldered back together.
Solid core mains cable stretches initially then becomes hardened over time. I have used everything from the wire out 2.5mm twin and earth to 16mm for ground radials without any problems.
My 17m dipole was made from heavy duty speaker cable from B&Q and the dipole centre is made from a block connector. It has been up for six years without a problem.
My 60m dipole has been up since 2006 and is made of .5mm PVC coated hook up cable.
My linked dipoles for portable work are also .5mm hook up cable.
The only commercial dipole I have is a G5RV that is made of Flexweave and that has had two breaks in it. Breaks in Flexweave seem to be caused by kinking and what usually happens is the end support breaks or the antenna is taken down and the wire kinks then when you put it back up it breaks where it was kinked. I have soldered mine but it is ugly and you need to wear gloves when handling it due to nasty strands that will prick like thorns. I will replace the wire if I ever put it up again. I am unimpressed by the G5RV as an antenna and think that Flexweave is over-rated too.
The very best thing you can get is the stuff the army uses for dipoles, which has a strand of Kevlar running through it to stop it stretching or breaking. You sometimes see it on eBay.
Another good one is telephone wire. The stuff BT uses between their poles not the domestic stuff. It is multi-stranded with a strengthening strand of steel. You just need to solder all the multi stands together, but be careful that stuff can bite. It is quite stiff an can easily puncture the skin like a needle when you are bending or cutting it.
My advice is use what is to hand or what is cheap and mount every thing on a lanyard so it can easily be lowered for maintenance or replacement.
Hope this helps. Please don’t waste money on expensive wire or antennas it is the one area where the amateur can do as good or better than the professional.
Regards Steve GW7AAV