The invention provides a process of producing a mineral wool growth substrate comprising providing a charge of solid mineral material, melting the mineral material to form a melt, forming fibres from the melt and collecting the fibres as a primary web, and consolidating the primary web, the process comprising applying to the fibres, after formation and before collection, binder and wetting agent, wherein the wetting agent comprises ionic surfactant, characterised in that substantially no polyol is applied to the fibres after formation and before collection.
