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?