Sentimental Dutch material (5)
I believe the answer is:
tweed
'material' is the definition.
(I know that tweed is a type of material)
'sentimental dutch' is the wordplay.
'sentimental' becomes 'twee' (I've seen this before).
'dutch' becomes 'd' (common abbreviation).
'twee'+'d'='TWEED'
(Other definitions for tweed that I've seen before include "passes between English and Scottish banks" , "Boundary river" , "flows across a border" , "Flow" , "Rough material" .)