The material is nice? He'll ruin it (8)
I believe the answer is:
chenille
'the material' is the definition.
(chenille is a kind of material)
'nice? he'll ruin it' is the wordplay.
'nice? he'll' can be anagrammed to 'CHENILLE'.
Though, I'm not sure how the anagram is indicated.
'is' is the link.
Can you help me to learn more?
(Other definitions for chenille that I've seen before include "Velvety cord used as trimming" , "Hellenic (anag) - material" , "Tufted velvety cord or yarn" , "Hellenic kind of fabric with long velvety pile" , "Velvety cord used in clothing, carpets etc - Hellenic (anag)" .)