Improvements in security papers and documents

The present invention is directed towards a security paper 10 comprising at least one layer 11 of fibrous substrate and a security additive 14 embedded within the fibrous substrate. The security additive is located within a predetermined region of the at least one layer and at least 75% of the security additive in the predetermined region is fully embedded within the at least one layer. The security additive is detectable when the fibrous substrate is split, thereby exposing the security additive. A security document comprising the security paper is also claimed, wherein the security document is selected from a banknote, a cheque, a certificate, a passport, a passport page, an identification card and a drivers licence. The present invention further provides a method of manufacturing the security paper, wherein the method comprises depositing fibres to form a fibrous substrate on a support surface; depositing the security additive on an initial layer of fibres; depositing further fibres over the security additive and the initial layer to form an integral layer of fibrous substrate; couching the layer of fibrous substrate and security additive from the support surface; and drying the layer of fibrous substrate and security additive.