The textures and microstructures of three different experimental mesop
hase pitch-based ribbon fibers were studied using the complementary te
chniques of scanning and transmission electron microscopy and wide ang
le X-ray diffraction. The effect of mesophase pitch precursor and capi
llary entry design on the structure and heat transfer capabilities of
these ribbon-shaped fibers was investigated. It was found that ribbon
fibers melt-spun from a synthetic, naphthalene-based mesophase had hig
her degrees of preferred orientation and graphitization, larger crysta
llite sizes and lower electrical resistivities than those of fibers me
lt-spun from a petroleum-based, heat-soaked mesophase. However, capill
ary entry design proved to be critical to the development of a more li
near transverse texture and a structure that one might expect to be mo
re conducive to axial heat transfer.