From Science Teacher (and carp-guide extrordinaire) Joel Hays:

hey Bart –

cool stuff! Now, here’s some real chemical geekness . . .

Boron has never “taken off” as a sole rod component because of its goofy metalloidal proprties. It’s in the same group as aluminum and shares similar proprties like incredibly high strength-to-weight ratio. And, it’s a smaller atom than carbon so you think that would extrapolate out to a lighter rod. Unfortunately, the bonding characteristics of boron make it difficult to produce a small fiber. A boron fiber IS very strong, but it’s also big. One boron fiber is about 15-20x larger than a carbon fiber (it’s about the same size as a fiberglass “S”glass fiber).
When a manufacturer like Winston uses boron, it’s usually sandwiched between two graphite sheets, and usually only in the butt section. What boron probably DOES give you is some great dampening characteristics as well as a favorable strength to weight ratio. Other manufacturers achieve the same result with more,”finer” graphite fibers in ever-increasingly complex lay-ups (like the TCX!).
what a geek!