Block request for material (6)
I believe the answer is:
damask
'for material' is the definition.
(damask is a kind of material)
'block request' is the wordplay.
'block' becomes 'dam' (damming is a kind of blocking).
'request' becomes 'ask' (to ask is to request something).
'dam'+'ask'='DAMASK'
(Other definitions for damask that I've seen before include "Fine linen with woven pattern" , "Table linen material" , "Patterned material" , "Heavy embroidered linen" , "Fabric used for table linen" .)