Implementing protective features directly into the mass of the paper takes place during the production of the paper. There are two types of protection:
A watermark is an image, text, or any other desired design. It is integrated into the paper during its production by impressing the paper fibres. This changes the paper thickness. The impressed element is visible by human eye if the paper is held against the light.
These are coloured fibres which are embedded or dispersed into the paper structure during the manufacturing process. They may be metallic, cotton, transparent or they can be seen as fluorescent under a UV light.