Keen about demand for patterned material (6)
I believe the answer is:
damask
'patterned material' is the definition.
(I've seen this before)
'keen about demand' is the wordplay.
'keen' becomes 'mad' (both can mean enthusiastic about).
'about' is a reversal indicator.
'demand' becomes 'ask' (synonyms).
'mad' reversed gives 'dam'.
'dam'+'ask'='DAMASK'
'for' is the link.
(Other definitions for damask that I've seen before include "Silk or linen material woven with pattern on either side" , "Table linen material" , "reversible material" , "Type of table linen" , "Cloth, originally Syrian" .)