Hi-Vi Research F6 Woven Kevlar/Paper Cone Woofer.
The 6.5″ woofer has been around for a while. The sound from it is very good and perhaps it is not used much because of the yellow cone color.
This has recently been used in a very nice kit by Ben Shaffer called the “Nephila”. At a recent, judged audio fest, it won it class and comments from the judges included “Easily, a viable commercial product”.
The cone material is a Kevlar impregnated paper with rubber surround and housed in an aluminum basket.