Ive never owned a curly, but from what I have heard and seen from pictures, they seem to have sparse feathering.
http://www.feathersite.com/Poultry/CGD/Friz/WhatMakesFriz.html says:
......Thus, the reason for not breeding Frizzle to Frizzle: It causes the bird to have less feather follicles and thus will cause the bird to come out with a dozen feathers and be bald over the body and intolerant of the sun or the cold weather. Curlys are a no-no in the Frizzle breeding.
There is more info there if you want to read it!
http://www.feathersite.com/Poultry/CGD/Friz/WhatMakesFriz.html says:
......Thus, the reason for not breeding Frizzle to Frizzle: It causes the bird to have less feather follicles and thus will cause the bird to come out with a dozen feathers and be bald over the body and intolerant of the sun or the cold weather. Curlys are a no-no in the Frizzle breeding.
There is more info there if you want to read it!