Boron has never been uses in any rods in a very high percentage due to it
inherent problems, the biggest being that the fibers are many times larger
than the fibers on a graphite sheet, this leaves more area betwwen the
fibers for excess bonding resin that make the rods much more liable to
fracture or delaminate between the fibers.
Titanium is usually just added to the resin and benefits nothing.
Quartz Matrix scrim and other innovations are in the works that look more
promising.