Roving is wool fibre that has been processed so that all of the fibres are going in one direction, It tends to be smoother and has longer fibres than carded wool. It is still versatile though and can be used for flat and 3D projects. If using it to bulk out 3D work I would suggest messing up the fibre first and getting the fibres going in all different directions. Strangely enough this helps give you a smoother finish and a more consistent felt.