Crossword Genius

Answer SOS to protect finest building material (8)

Ross

I believe the answer is:

asbestos

'building material' is the definition.

'answer sos to protect finest' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'to protect' indicates putting letters inside.
'finest' becomes 'best' (similar in meaning).
'sos' going around 'best' is 'sbestos'.
'a'+'sbestos'='ASBESTOS'

(Other definitions for asbestos that I've seen before include "Heat-resistant material" , "I might end up lagging" , "retardant" , "Fire-resistant material, injurious to health" , "Fireproof material, now known to be dangerous" .)

I've seen this clue in The Telegraph and The Sun.
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