Most of today's high-end cinema cameras do not come equipped with a built-in low-pass or IR cut filter since they try to mimic the human eye and receive as much data as possible from the image subject. The more sensitive cameras are to light, however, the more exposure needs to be maintained using a stronger ND filter which in turn creates infrared pollution. To alleviate this issue, many camera manufacturers recommend the use of an IRND filter, even though many of the IRND filters on the market today have adverse side effects that come along with them such as color shifting. In addition to this, after adding or replacing an IRND filter, the white balance needs to be adjusted to maintain true color fidelity, which can quickly become too much work. In the end, the benefit of cutting infrared pollution doesn't seem like much of a benefit considering the need to continually white balance during a shoot and then correct color shifts in post.
In terms of the development team at Kenko Tokina with their innovative Accu-ND Technology, creating a Neutral Density filter that precisely controls the amount of light entering the lens without affecting the color. A revolutionary filter that stabilizes the transmittance of color throughout the visible spectrum.
The square/rectangular type of filter has an ND vapor deposition coating sandwiched between two layers of glass so the filter can be re-polished again and again should it get scratched, extending the life of the filter.