There are various values that catch your eye when looking for a suitable down duvet — for example the weight, the ratio of down and feathers or the bulkiness.
The CUIN value (CUIN = cubic inches) indicates the bulkiness of the down. It is an international unit of measurement for down quality.
For the same weight, down with a higher CUIN value is more puffy, voluminous and therefore fluffier. The higher the CUIN value, the higher the warmth and insulation performance of the down. Thus, duvets filled with 800 CUIN down warm us better than duvets filled with 400 CUIN down.
How is the CUIN value determined?
A CUIN value of 800 means that 28g of down expands to a volume of 800 cubic inches. The 28g of down is filled into a cylinder and compressed for 24 hours. Then the pressure on the down is removed and it is seen how well the down now returns to its original state. This is how the filling power of the down can be determined.