Down is unrivalled when it comes to outdoor gear insulations.

Let us tell you why as we take you on a very special journey. Guiding you through down’s history, exploring how it works and where its properties come from, we’ll make sure you have all the know-how necessary to choose your long-lasting professional equipment.

What do you need? A thirst for knowledge and a cosy moment with a cup of tea or coffee. In times of short messaging we present you something different – a long and extensive piece covering the topic inside out. This guide is as friendly as possible but it’s an in-depth tour that will take more than few minutes. So hold on tight as we tell the story.


It was only in the second half of the twentieth century that down’s properties were discovered by outdoor enthusiasts. The secret behind down’s growing popularity and widespread use is the fact that it’s the most effective available insulation in the world.

We must remember that it stems for aquatic, migrating birds. It comes from geese, birds that can fly hundreds of kilometers at high altitude in low temperature.

What down has to offer is a unique combination of the weight to warmth ratio. There’s lot of insulating solutions in the world but down’s thermal insulating properties outperform all natural and synthetic products known to humanity.

This fact has been noted by the outdoor industry. Down fillings, reliable, light and effective, quickly became the insulation of choice for all outdoor professionals.

Today, despite all the innovation, technological advancements and new lighter fabrics boasting a high resistance, there is still no synthetic insulation that offers parameters resembling those of the goose down. It is simply unbeatable.

Down is the reason why we can offer you products that are a combination of lightness and thermal efficiency. We are also proud to say that at Cumulus we only use ethically sourced Polish down, which is considered the best in the world.

Let us now show you how this insulation works in practice.

Where do down’s insulative properties come from?

It’s actually a simplification when we say that down insulates, as the way things work is as follows: thanks to its structure, down can retain a lot of air and it is the air that isolates the user from cold. Down is extremely dense and its feathers are little works of art made up of thousands of microfibers that have a complicated structure. When the air is trapped between the feathers, it becomes still, thus creating an insulating layer. The less movement of the air, the better the insulation.

How to analyse down parameters when evaluating products?

Down’s loft or ‘fluffiness’ is described by either cubic inches (CUIN) or fill power (FP). This parameter describes how many cubic inches are filled by one ounce of down (28 grams). What it shows in practice is how much air can be trapped. The higher the fill power, the more space the down will take up, at the same time providing a better insulation.

Let us look at an example

Interesting facts

-> The jacket on the left will have the same parameters as the one on the right on the condition it has a bit more of 700FP down. However, as a result it will weigh more.*

-> Don’t expect that down with a higher fill power will take up less space in your luggage than down with lower fill power. That’s a common, yet false assumption. In reality, the better the down, the more space it takes and the better its insulating properties. This refers both to compressed and loose down.

-> It is also a popular belief that 700 fill power is more durable than down with a higher fill power. However there is no research or scientific data to back up this theory.

* almost the same, as higher fill power needs slightly larger chambers which slightly affects the product weight.

Optimal parameters

Down’s density and its spacial proportion to the chamber it fills is the key to creating an optimal layer of insulation. For example stuffing 500 grams into a sleeping bag whose chambers were designed for 200 grams doesn’t make any sense. The down will become too dense, extreme thickness will prevent it from acquiring its loft and optimal density. The same is the other way round, namely if you take a big chamber and fill it with too little down. The filling might become unsymmetrical and bumpy, leading to “cold spots” and a gradual decrease in insulation efficiency. So both parameters must be matched.

Another key parameter is the down to feather ratio, which is described by two numbers e.g. 94/6. This first number refers to the percentage of down (in this case 94%) and the second one represents the percentage of feathers (6% respectively). These are feathers that have not been separated from down in the production. You can recognize them by a thick root. Down traps more air than feathers. So the fewer the feathers, the better the down quality.

Practical advice

If you’re looking for light outdoor gear, consider products with high fill power. They give more comfort at low weight, allowing you to move easier and faster.

Should I only look at fill power when buying products?

No. When choosing down products, it’s also important to have a look at the amount of down put inside (down weight). This is another important parameter to look at that will allow you to compare products. If the producer doesn’t provide this information it’s impossible to tell which product will be warmer.



When should I consider hydrophobic down?

Down absorbs water very easily therefore it should be protected from humidity as much as possible. When wet, down loses its insulating properties.

Hydrophobic down is a solution to this problem. In this process down is treated with special impregnating agents. This ensures higher resistance to moisture and faster drying.

Hydrophobic down used together with a waterproof fabric highly prolongs the life of outdoor equipment such as sleeping bags or jackets. Nevertheless if possible, such products still should be protected from damp.

Hydrophobic down lasts 5 to 6 washings. This allows us to enjoy the product for a few years as sleeping-bags and down gear is generally not washed that frequently. There’s also a good choice of special agents that allow down to regain its hydrophobic properties. Considering that a product is usually washed once a year, this solutions nicely extends its lifespan. What’s more down that has lost its hydrophobic qualities is still perfectly good for use in dry conditions. The hydrophobic down used by Cumulus is PFC free.

Down in our products

FP700 – 100% ethically sourced Polish goose down, for those who expect quality and pay no attention to minor differences in product weight

FP850 – 100% ethically sourced Polish goose down of fantastic compressibility used in the majority of our products; the insulation it provides is impressive when compared to product weight or price

FP900 – 100% ethically sourced Polish goose down used only in our lightest products, made for the outdoor enthusiast who has a zero excess weight policy// made for the outdoor enthusiast for whom every bit of weight is a concern

Down Clothing & Sleeping Bags Practical Advice


In outdoor apparel, the most important insulation is synthetic insulation (such as Primaloft or Climashield) and natural down. Down is a great solution when the physical effort is moderate and your body does not evaporate a lot of water (when you don’t sweat excessively), for example when waiting at a belay station, pausing in a hike, or during a brisk walk. It is also great at night as it gives that extra warmth and protection. As your body does not warm up during such activities, the clothing provides the necessary insulation. If you sleep in down gear, you can carry a lighter sleeping bag.

Unfortunately, it is impossible to say how warm you will be in different clothing as there are lots of elements responsible for body temperature. Among the most important ones to look at are whether it’s windy or not and if so how strong the wind is, it’s also important whether you’re still or moving, how many other layers of clothing you have and how tired your body is.

Down gear is generally very reliable although it should be used differently in different conditions. For example our Inverse Jacket, filled with mere 60 gram of down will be a great choice as an extra layer even when the temperature drops below – 20C. At this temperature even one layer of clothing and just 60 gram of down can make a big difference. When it gets warmer, say at 5C, Inverse can be your primary jacket that you put on when camping or resting.

When it comes to outdoor clothing we are big fans of ‘the layering system”. Hybrid jackets that are multifunctional e.g. waterproof with a down lining are not a good solution, it is much better to pack a few different items that play different roles. Combining layers of clothing allows you the flexibility to find an optimal solution, adequate for outside weather conditions. Down gear should be the main insulating layer. In dry conditions it can also become the outer layer.

Sleeping bags

Things are easier with sleeping bags. A down sleeping bag will always be lighter and more compact than a synthetic one so it is the better choice. There is only one exception to this rule: if there’s a risk your sleeping bag can get completely wet and there will be limited opportunities for drying it, lasting even up to a couple of days, then a synthetic bag should be your product of choice. Nevertheless, if you still insist on a down sleeping bag, one of our bivy bags can provide some protection from water and it’s also possible to have a made-to-order sleeping bag with an outside waterproof layer.

What’s so special about Polish goose down?

Polish goose down is considered the best in the world and there’s a few reasons behind it.

SCIENCE – Decades of research and a good scientific background resulted in creating down of superb quality. Observation and years of improvements brought real knowledge on breeding best geese in optimal conditions.

CLIMATE – Polish climate with its characteristic warm summers and cold winters is conducive to growing strong flock that boasts superb feathers. Neither cold or warm weather is the key here but the amplitude of temperature changes during the year

BREEDING CONDITIONS – Polish geese enjoy some of the best breeding conditions, they are free-range animals, that have constant access to water and air. Such conditions are the secret behind their strong feathers.

RESPECT – Polish farmers do not interfere with the animals’ natural life cycle. They respect nature with its cycles of growth.

This is why Polish down remains unrivaled. Producers all over the world appreciate its quality and turn to Polish suppliers when looking for down fillings that boast high performance parameters.

100% Ethically sourced

At Cumulus we use only white Polish goose down that is 100% ethically sourced. We cooperate with Poland’s two main down suppliers that collect down from smaller farms.

As we are allowed to track the production process we are sure that all the down used in our products meets our environmental standards, there’s no life plucking and high animal welfare standards are maintained. We believe that the true outdoor enthusiast always respects nature. That goes as well for the production process of every Cumulus item.