The filling power – measured in CUIN – is the primary scientific standard for the quality of the down. The higher the filling power, i.e. the CUIN value, the better the quality.
At the same weight, first-class down is several times more voluminous with a much greater filling power, making it fluffier. The duvet is perceptibly lighter with the same thermal performance. The best duvet is the one which has the highest thermal insulation property at the lowest weight.
