Fibres for protective coat and top stocked by fashion e-tailer (8)
I believe the answer is:
asbestos
'fibres for protective coat' is the definition.
(material used as insulation)
'top stocked by fashion e-tailer' is the wordplay.
'top' becomes 'best' (similar in meaning).
'stocked by' indicates putting letters inside.
'fashion e-tailer' becomes 'asos' (online fashion retailer).
'best' put inside 'asos' is 'ASBESTOS'.
'and' acts as a link.
(Other definitions for asbestos that I've seen before include "Survivor of heat" , "Fibrous mineral, used as an insulator, now deemed harmful" , "risky material" , "Fire-resistant material, injurious to health" , "we now know to be dangerous" .)