This article explains it in detail a lot better than I could...
From the gibson.com site:
"For years, fretboards have been made out of wood because frankly, nothing was better. But then 70 years ago, there was a need for a wood replacement in aerospace and other industries where hardness, consistency, and smoothness had to be perfect. A new option called Richlite, which was based on wood products but much stronger and consistent, was developed and quickly became popular for demanding applications.
Gibson USA has always been about creating a better guitar, and back in the mid- ’90s started looking into whether there might be comparable alternatives to the conventional fretboard. None of them really panned out except for Richlite, which appeared promising. However, the question of whether to use a different fretboard material wasn’t a question to be taken lightly.
After two decades of research and discussions with guitarists, Gibson determined that Richlite was not only the best alternative to woods like ebony, but was actually superior. Although the downside is that it’s more expensive to make guitars with Richlite fretboards than ebony, there are some very attractive benefits.
This Richlite fingerboard on the Gibson SG Light 7 has the look and feel of ebony, but offers several advantages.
Perhaps most importantly, the quality is consistently high—you don’t have to wade through batches of Richlite to find “good” Richlite. Also, many guitar players feel strings bend more smoothly on a Richlite fingerboard, and tonally speaking,
virtually no one can tell the difference in a blind test. Another little-known advantage is with white guitars. The pigments in rosewood and ebony can “bleed” during the finishing process, and end up coloring the white finish. Richlite won’t do that; it’s also scratch, heat, and stain-resistant, as well as being non-toxic, non-warping, and made in the USA. Finally, neck bow issues are less likely because you don’t have two different wood species expanding and contracting at different rates, and frets don’t loosen due to wood shrinkage.
Think of it this way: if guitars had
always been made with Richlite and someone figured out you could use ebony, it’s doubtful people would want to switch to a material that created problems instead of solved them. The many positive comments on message boards from guitar players who have used both ebony and Richlite confirm that for playability and functionality, Richlite is at least equal to ebony—and many guitarists even prefer it. In a world where ebony is becoming increasingly problematic, that’s good news for those us who love to play guitar."
http://www.gibson.com/News-Lifestyle...ngerboard.aspx