Rope fibre (4)
'rope fibre' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sisal that I've seen before include "Agave cultivated for its fibre" , "Rope-fibre made from leaves of tropical plant" , "Agave rope-fibre" , "Ropemaker" , "Strong rope fibre" .)
(Other definitions for oakum that I've seen before include "What convicts used to pick" , "ropy bits" , "One hand-picked" , "Rope fibre for caulking wooden ships" , "Fibrous material from rope" .)
(Other definitions for coir that I've seen before include "Coconut husk fibre used for making matting" , "Coarse fibre from a coconut husk" , "growing medium" , "Fibre from coconut husks" .)