Rude to limit area for protecting (10)

I believe the answer is:

insulating

'protecting' is the definition.
(insulate can mean to protect)

'rude to limit area' is the wordplay.
'rude' becomes 'insulting'.
'to limit' is an insertion indicator.
'area' becomes 'a' (maths abbreviation).
'insulting' going around 'a' is 'INSULATING'.

'for' acts as a link.

I've seen this clue in The Guardian.

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