Gaseous
I'm not sure if ebay sellers may be getting confused (or don't know the difference) between aramid carbon fibre and kevlar.
Mine is military spec and it's definately carbon on the inside layer that I can see.
However, it may be layered in both carbon
and kevlar (kevlar sandwiched in the middle).
Either way, as a general rule, carbon gives rigidity and strength, and kevlar gives flexibility and strength, so to answer your question - in theory, a carbon/kevlar helmet is better than a purely carbon helmet because it gives better impact absorbtion i.e. the kevlar allows the helmet to 'give' a little if you take a bump on the noggin!
Having said that, the guys at Alpha know alot more about helmets than I do, so what ever they have done must be right!
P.S. My knowlege of carbon/kevlar composites comes from the racing industry, so it may be completely inaccurate for helmets!