The literature on stain blockers, which are employed for reducing the staining of nylon fibres used in carpeting, has been reviewed. These compounds include the reaction products of sulphonated phenolic compounds and formaldehyde. They may be applied as a spin finish immediately after the extrusion of the nylon fibres or to the fibres after the carpets have been made. The composition of stain blockers, the methods of application to nylon fibre and the resulting properties are described. Mechanisms to explain the action of stain blockers are discussed.