Generally the feather length and softness determines the fluffiness. Short feathers just do not fluff out as much, and harder feathers (think cornish versus cochin) tend to lie close to the body, also taking away from the fluffiness. Breeders tend to not use birds that are not as fluffy, or that have too many non-silkied or hard feathers, so the offspring are less likely to inherit those genes. Hatcheries care about quantity, not quality, and so you will find many silkies who are lacking in fluffiness--becuase their parents did not cave those traits in abundance. Some lines of silkies have extra dense feathering, also--as in more feathers per square inch. Both the APA ad ABA have a standard for silkies; they are very similar. Both bearded and non-bearded varieties are recognised.