kh seat fabric why?

why do the kh seats have that fabric on them it ?¿?¿?¿
also is it possible to convert coventionle kh seats to air or gel?

Presumably because KH figured given the important parametres that was the best fabric to go with, and which fabric do you mean? each seat has atleast two different fabrics on it and there have been lots of different fabrics used over the years. It is possible to convert one to air or gel, dismantle your seat, make a suitable cutout in the foam, insert either a gel insert or an inner tube in a sock or special airseat pillow in the cut-out you just made, remantle the seat, job done.