I once spoke to an engineer at Visaton, and he told me that they were using a proprietary blend of manila, a grass indigenous to South Asia, with similar tensile, and elastic properties to hemp, and a small amount of carbon fibers. It is an unbelievably tough cone material.
The "hemp" sound has to do with John Harrison's proprietary recipe using hemp fibers. The B200 and FR8 are quite similar sounding in the midband, in my opinion.