This is the seventh in a series of articles on synthetic fibers and how they relate to shaving brushes, including a brief history of synthetic fibers, their development, stagnation, and resurrection in the market place. We are now at a point where a need was increasing for substitute synthetic fiber that could retain (not absorb) liquids to mimic natural hairs in cosmetic brushes. Many patents were made on the subject but in 1979 a team of inventors from Toray Industries developed a process for shaping synthetic fibers to closely resemble the function of natural fibers to be used in both brushes and fabrics.
United States Patent 4,381,325 provides some insight into this development:
This invention relates to a liquid retaining synthetic fiber having a substantially pointed free end and including a tapered portion having an acute ridgeline on its surface. It is prepared from a synthetic fiber having in section at least one concave portion and at least one convex portion which gradually taper off toward the outside from the center.
These fibers are suitable for use in brushes, or for the manufacture of knitted or woven fabrics or flocked fabrics having an animal hair-like or fur like touch or appearance. 
For the sake of brevity, since this patent has many pages of detailed information, the following excerpts have been taken to discuss the overall breakthrough of the new fiber shaping technology.
Animal hairs having so-called tapered or sharpened ends are now used in various fields and articles, including brushes such as writing brushes and painting brushes made from hairs of weasels, raccoons and the like. Further, hairs such as those from Angora rabbits and the like have been mix-spun and incorporated into knitted or woven fabrics. Another well known use is in furs such as mink, fox, and the like.
These animal hairs, however, are very expensive, and extensive efforts have been made to produce synthetic fibers having their desirable characteristics have heretofore been proposed…
Fibers according to the present invention are tapered or sharpened synthetic fibers each having a substantially pointed free end and including a tapered portion having an acute ridgeline extending longitudinally along the fiber surface.
Fibers of this invention may be made into brushes comprising sharpened synthetic fibers having substantially pointed free ends, the fibers including tapered portions having a sharp or acutely curved ridgeline extending longitudinally along the body portion of the fiber, preferably to its tapered end. 
The problem with synthetic fibers at the time of this invention was that the material was solid and would not absorb any liquid like natural hairs would (some with a greater level of absorption than others). With this invention, synthetic fibers could be formed to provide “channels” to hold liquids, creams and even powders, provided that there is enough density of fibers in the brush. This along with another modification of a synthetic substance called Taklon provides, along with Nylon, two different fibers for synthetic brush making.
DuPont invented the process of making Taklon, in which polyester fiber is extruded and tapered to a fine point. DuPont sold the rights to this process to the Toray Chemical Co. of Osaka Japan. Taklon was originally designed to mimic the handling characteristics of natural sable. 
So now the major elements for making synthetic brushes were in place. Multiple synthetic materials, flagged ends versus tapered ends, channelized fibers to better retain product were available to be experimented with. Over the years the cosmetic industry continued to refine and develop the fibers and brushes to provide low end cosmetic brushes. As time went on, increasingly higher end brushes were produced from synthetic fibers. Meanwhile traditional shaving still relied upon natural hairs for many years to come due to the limited demands on traditional shaving products in the market place. The next major milestone in the development of shaving brushes will occur after a change in how the world communicates comes into full effect. These changes will be examined in future installments of this series.
  U.S. Patent number: 4,381,325 Filing date: Sep 8, 1980 Issue date: 1983