In article ,
Urman writes:
I am in the UK and have an old portable electric heater.

The mains flex to the heater is like that to a domestic iron: woven
fabric outer overlaying a rubber (?) outer sheath. With each of the
three leads covered in rubber insulation and three cords running
alongside the three leads.

(1) Is the fabric outer to make the flex resistent to KINKING? Or is
it there for HEAT PROTECTION?

(2) Is the RUBBER used in this sort of flex especially resistent to
TEMPERATURE?

(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?

The answers to these questions have completely changed over time.
Back when your heater was bought, the cotten cover improved the
heat resistance of the cord against coming in contact with hot
surfaces. Nowadays, various types of man-made rubber can survive
higher temperatures than cotten so it's no longer used for this
purpose.

However, you'll still find cotten covering on iron cords. The
reason for this is that rubber cords catch on the fabric you are
trying to iron and move it on the ironing board, whereas the
cotten covering helps reduce the effect as it slides easier
against fabrics.

--
Andrew Gabriel