Some of the products we sell at SuperLigero.es are filled with natural goose down up to 900 cuin.
But… what does Fill Power 900 cuin actually mean?
I asked myself the same thing when I started buying my first down clothing for the mountains.
In this article I want to explain, in a simple way, what Fill Power means, how it’s measured, and why it matters so much when you’re choosing a jacket or a sleeping bag.
Air is the real insulator
To understand how down works, you first need to understand how thermal insulation works.
Air is fundamental.
Heat is transferred when there is air movement. That’s why we use a wind jacket: to stop cold air from getting in and carrying away our body heat.
Down Quality: What Fill Power and CUIN Mean
Learn what Fill Power and CUIN mean in down. Discover how down quality is measured and how to choose the best insulation for the mountains.
Some of the products we sell at SuperLigero.es are filled with natural goose down up to 900 cuin.
But… what does Fill Power 900 cuin actually mean?
I asked myself the same thing when I started buying my first down clothing for the mountains.
In this article I want to explain, in a simple way, what Fill Power means, how it’s measured, and why it matters so much when you’re choosing a jacket or a sleeping bag.
Air is the real insulator
To understand how down works, you first need to understand how thermal insulation works.
Air is fundamental.
Heat is transferred when there is air movement. That’s why we use a wind jacket: to stop cold air from getting in and carrying away our body heat.
This phenomenon is called convection.
Insulating materials work by trapping air inside them.
The more air they can hold, the better their insulating performance.
That’s why fibrous or porous materials, like down, are excellent thermal insulators.
Feathers vs down
Not all feathers are the same.
Many manufacturers use a mix of feathers and down in their products.
But there’s an important difference between the two.
Down is the part that actually provides insulation.
It’s a very light, three-dimensional structure that traps large amounts of air.
Traditional feathers have a stiff central shaft and provide much less insulation.
That’s why a garment with:
90% down / 10% feathers
is not the same as a garment with:
60% down / 40% feathers
The higher the percentage of down, the higher the insulation quality tends to be.
What Fill Power (CUIN) means
The Fill Power measures down’s loft.
In other words, how much volume a given amount of down can occupy.
This is expressed in CUIN (cubic inches per ounce).
The higher the CUIN number, the more the down can loft and trap air.
This means:
For example:
Some specialist manufacturers even use 1000 cuin down in highly technical garments.
How Fill Power is measured
Fill Power is measured using a standardized method.
About 30 g of down is placed into a transparent cylinder and a controlled pressure is applied.
The pressure is then removed and the volume the down reaches as it lofts is measured.
That volume is expressed in CUIN.
The more volume the down reaches, the higher its Fill Power.
Fill Power vs amount of down
Fill Power indicates down quality, but not how much down a garment contains.
To understand the real warmth of a jacket or sleeping bag, you need to look at two things:
For example:
A jacket with 100 g of 900 cuin down can offer similar insulation to one with 160 g of 650 cuin down.
The difference is that the first will be lighter and more compressible.
That’s why ultralight gear usually uses higher-quality down.
Down classification by Fill Power
Hydrophobic treatments
In recent years, some manufacturers have developed hydrophobic treatments for down.
These treatments help down retain its loft better in damp conditions.
One example is treated down such as QShield Down, used by some manufacturers in sleeping bags.
Ethical down certification
Many manufacturers today use down certified under the RDS (Responsible Down Standard).
This certification ensures the down comes from animals that have not been subjected to practices such as live-plucking.
Why high-quality down costs more
Higher Fill Power down is rarer and harder to source.
That’s why garments with 850 or 900 cuin down usually come with a higher price tag.
But they also offer a clear advantage: more warmth for less weight and less bulk.
And when most of your kit spends its time inside your pack, you’ll appreciate that.
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