Money? Nothing but woollen material (8)
I believe the answer is:
cashmere
'woollen material' is the definition.
'money? nothing but' is the wordplay.
'money?' becomes 'cash' (cash is a type of money).
'nothing but' becomes 'mere' (I've seen this in another clue).
'cash'+'mere'='CASHMERE'
(Other definitions for cashmere that I've seen before include "'Fine, soft wool from a goat (8)'" , "Woolly stuff" , "Fabric from fine goat's wool" , "High-quality wool" , "Expensive material" .)