Cuin is a measure of the insulation factor/power in any down product. Cuin is short for “cubic inches”. So, the count for the individual product in cuin is the amount one ounce takes up in cubic inches in a standard measure tube. Nordisk down sleeping bags go from 600 cuin up to 800+, which means that one ounce down in e.g., Phantom 220 takes up 700 (EU) cubic inches. The higher the cuin, the finer the down, the more air the down traps within it. Another term for this is Fillpower/loft.