The sisal is very rough. It must be charged with paste for pre-polishing and semi-finishing.
Its' texture does not permit to obtain a bright finish, even if used with a finishing paste.

The cotton layers are sewed together to form a polishing disc. Several concentric sewings assure a very good shape-keeping of the disc.
The sewed cotton is less supple than the layers of cotton which are fixed between mounting plates and is always suppler than a polishing felt.
There is no rule, which gives preference to the sewed cotton instead of the layers of coton that need to be fixed between mounting plates. It is the users's choice.
The sewed cotton discs can be piled up to create larger discs. They can equip your grinding machine.
The non-sewn discs are to be used in packs" between mouting plates.