Balzac said half should be cut - it's very lightweight material (5)
I believe the answer is:
balsa
'lightweight material' is the definition.
'balzac said half should be cut it's' is the wordplay.
I cannot really see how this works, but
'it' could be 'sa' (old-fashioned abbreviation for sex appeal) and 'sa' is present in the answer.
The remaining letters 'bal' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'very' is the link.
Can you help me to learn more?
(Other definitions for balsa that I've seen before include "Wood used in model making" , "Lightweight timber" , "Model makers use it" , "Very lightweight wood from tropical tree" , "wood for raft" .)