Corded fabric (5)
(Other definitions for twill that I've seen before include "Material" , "Fabric woven to have diagonal ribs" , "Cloth with diagonal ribs" , "Strong ridged fabric" , "Ribbed cloth" .)
'corded fabric' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rep that I've seen before include "Representative; fabric" , "agent" , "Repertory theatre" , "Corded fabric" , "Salesperson" .)