We know that the fibres take care for the transport of water through the substrate.At the other hand, water will drain out of the substrate more easy because the water-holding-capacity of the material is very low. Also we know that Coco-fibre makes the substrate more elastic.
For that reason we say:
YES, Coco-fibre improves the structure of the Grow-bag.
BUT, not for longer cultures, than it might turn against you.
Explanation:
Cocopeat and Coco-fibre contains lignine and cellulose. Lignine is wood and is hard, cellulose is soft material. Compared to Coco-pith, the Coco-fibre contains more cellulose and less lignine. This means that Coco-fibre will decompose faster than Cocopeat. How fast it will decompose depends on the circumstances during growth and on the thickness of the fibre. Thicker fibre has a smaller surface per weight end will break down more slowly. This means Coco-fibre is not usable to have a positive effect after several years in a crop like roses. It will only have a short-term effect (1-2 years). For that reason, Dutch Plantin advises a 1/4 inch sieved material which looks finer but the air content is much more stable than less-sieved material (1/2 inch or even 3/4 inch).