I purloined some of my wife's cotton balls only to find they weren't cotton at all. They don't even call them cotton on the bag - "Cosmetic Puffs" was the name on the bag. The cosmetic puffs are some type of synthetic and they light easily with a spark and burn hot emitting a deep black smoke.

I suspect one of the reasons that dryer lint works so well is because it is a mixture of tiny bits of different types of material, some of them synthetic.