Plastic switch needed for telephony (9)

I believe the answer is:

polythene

'plastic' is the definition.
(I've seen this before)

'switch needed for telephony' is the wordplay.
'switch needed for' indicates an anagram.
'telephony' anagrammed gives 'POLYTHENE'.

(Other definitions for polythene that I've seen before include "Synthetic 6 Dn" , "Strange telephony provides a lightweight material, used in packaging" , "Packaging material -- telephony (anag)" , "Synthetic resin" , "A lightweight thermoplastic" .)

I've seen this clue in The Guardian.

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