So donate it to a museum or scrap yard.
| The mains flex to the heater is like that to a domestic iron: woven | fabric outer overlaying a rubber (?) outer sheath.
Yes, it is vulcanized latex, better known as "rubber".
| With each of the | three leads covered in rubber insulation and three cords running | alongside the three leads.
The string is to prevent stretching.
| (1) Is the fabric outer to make the flex resistent to KINKING?
Yes. But it frays with excessive twisting/bending, usually where it enters the appliance. No need to shout.
| Or is | it there for HEAT PROTECTION?
No. Cotton is flammable.
| (2) Is the RUBBER used in this sort of flex especially resistent to | TEMPERATURE?
No. The cord or flex should be kept away from direct heat. After entering the appliance (iron, toaster, heater) the rubber sheath and fabric is stripped away and the conductors sheathed in a heat resistant material that also insulates, such as fibreglass.
| (3) Are the alternative materials (such as silicone rubber) used in | modern equivalents to this type of lead SUPERIOR IN ALL RESPECTS to the | sort of flex I have described?
In general, yes, material science has made improvements over older technology, although the techniques of insulation have changed little.
A neighbour of mine recently asked me if I knew of anyone interested in a Betamax VCR. I told him he had to be joking and found one on e-bay to show him, £0.99. If you want to use old technology, go the whole hog and light a coal fire, clean out the ashes each day and hire a chimney sweep on a regular basis - if you can find one - see Mary Poppins. Get a wooden clothes horse and dry your knickers in front of the fire. Otherwise find an empty space in a bin or scrap yard before you incinerate yourself and your family accidentally.
Androcles
(Note to Dork Van de merde: it's ok for *you* to use old appliances.)