On 05/07/2012 15:12, Nightjar wrote:

Nylon was invented about the same time as polyethylene, but AIUI the
latter had properties that made it particularly suitable as an insulator
when centimetric radar started to be used.

Yes, they're both good insulators at DC, but the dielectric properties
are chalk and cheese. Polyethylene and polystyrene are both low-loss
(non-polar) dielectrics at microwave frequencies, whereas the nylons
(polyamines) and PVC are polar and are about two orders of magnitude
more lossy at low frequencies, let alone at microwave.

An early use of polyethylene was for the dielectric in coaxial cables
(and it's still so used, of course).

PTFE (discovered 1938) is an even better dielectric, but I don't think
it was commercialised until after WW2.

--
Andy