Explosive material about creativity is sincere (9)
I believe the answer is:
heartfelt
'sincere' is the definition.
(similar in meaning)
'explosive material about creativity' is the wordplay.
'explosive' becomes 'he' (abbreviation for high explosive).
'material' becomes 'felt' (felt is a kind of material).
'about' says to put letters next to each other.
'creativity' becomes 'art' (creative work).
'felt' put after 'art' is 'artfelt'.
'he'+'artfelt'='HEARTFELT'
'is' is the link.
(Other definitions for heartfelt that I've seen before include "unfeigned sincerity" , "Let father have deep and earnest kind of emotion (9)" , "Profound" , "Sincerely intended with strong feeling" , "Deeply sincere" .)