Detailed suggestion promoting a material (7)
I believe the answer is:
apropos
'material' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for apropos that I've seen before include "To the point, germane" , "Touching" , "Appropriate" , "To the point about poor spa" , "To the point, relevant" .)