Strong polymer first produced by the DuPont firm in the 1930s (5)

I believe the answer is:

nylon

(Other definitions for nylon that I've seen before include "Synthetic material used in textiles" , "Fibre of polymeric amides" , "Artificial material" , "Fibrous material" , "Stocking; polymer" .)

I've seen this clue in The Mirror.

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