The neutral density filters (or DN) produce a neutral grey effect and are used to reduce the light in the photo, this allow the photographer a better control of the exposition and the deph of field without any color cast.
This filter is made from high quality optical glass (not resin) with nano coating to prevent losing any single bit of detail.
By using neutral density filter the camera is vulnerable to infrared light which will cast the unwanted red color to the photos when shotting at small aperture. Nisi added the infrared protection coating layer to this filter which help to eliminate the infrared light through the lens to bring back the nature color.
NiSi range cover the next filter dimensions: