This page provides information on the Corona Hair Modifier in 3ds Max.
Overview
The Corona Hair Modifier is used to control the "level of detail" of the hair geometry. By default, each hair strand is rendered as a flat 2D plane to achieve the best rendering speed at the cost of some realism. Using this modifier, you can force Corona to render hair as 3D tubes, which is useful for close-ups (e.g. eyelashes when the camera is zoomed in on an eye). Generally, for shots where the shape of each individual hair strand is not visible up close, it is best to use the default settings for optimal performance and quality.
Examples
By default, when the CoronaHairMod modifier is not used, hair strands are rendered as flat planes:
The CoronaHairMod modifier can be used to render hair as 3D tubes, which is useful for close-ups:
