Tell us about down:

  • 8 min read

Tell us about down:

Down is the layer of feathers that are closest to a bird’s body. These feathers are made of very fine tendrils and fibres that have evolved over hundreds of thousands of years to provide the lightest and most efficient means of trapping and holding air in position.

This trapped air produces an incredibly efficient thermal barrier, which at the weight and mass of down, is unrivalled by any natural or synthetic equivalent. By using down in the construction of garments and sleeping bags, we can ensure that your body heat stays put, instead of escaping into the atmosphere around you.

The individual down clusters expand, or loft, to fill an area that is vast relative to their size. Because the down consists almost entirely of trapped air, the result is a product that is incredibly light and also very easy to compress. Its down’s ability to pack down small into the pocket of a backpack or stuff sack that makes it the ideal insulation choice for climbers, mountaineers and anyone else who needs lightweight clothing.

Hydrophobic down

Down is naturally breathable, which makes it very comfortable to wear, but this comes with a drawback – it can absorb moisture.  This moisture can overload the fibres, or cause them to stick together, stripping the down of its insulative properties.

To mitigate this effect we apply a water repellent “hydrophobic” treatment to the down.  This treatment significantly improves the performance of the down by preventing the clusters from absorbing moisture and helping it to retain its loft.  In the event that the down does become waterlogged the treatment significantly decreases the time it takes the down to dry and its loft to recover.

It’s worth noting that hydrophobic treatment means that a down jacket will perform better in wet conditions, but it’s not intended to make a garment waterproof. If you’re looking for a down jacket that is also waterproof you’ll want something that combines insulation with a waterproof material, like our Valiance jacket which combines 800FP down with a Pertex® Shield outer fabric.

Down vs. Synthetic insulation

Broadly speaking our garments and sleeping bags use one of two types of insulation – down or synthetic. Although down is, for its weight, always warmer than a synthetic equivalent, there are instances where synthetic insulation may be the preferable choice.

Synthetic insulation is relatively good at dealing with moisture, especially when compared to down that has not been hydrophobically treated.  When synthetic insulation is soaked it will offer more warmth than down which makes it a good choice for damp and cold conditions, typical of Scottish winter climbing.

Synthetic insulation is generally easier to clean and care for and is also a less expensive material than down. Ultimately though, there is still no synthetic material that can rival the warmth to weight ratio of duck or goose down. So where weight and packability are a concern there is really no contest.

Duck and Goose down

Rab jackets use either duck down or goose down. Higher grade down (700FP and up) tends to be from geese as the clusters are larger, offering a higher warmth to weight ratio and improved packability. 

Although duck down consists of smaller clusters and a reduced warmth to weight ratio, we find that it is still the best choice for everyday jackets.  Jackets such as the Axion or Deep cover Parka use Duck down because premium goose down is simply too warm for everyday use. We also use duck down in our Asylum bouldering jacket because here, weight and packability are less of a priority.

Responsible Down Standard

While down products have revolutionised the way we dress for outdoor activities, it’s impossible to ignore the fact that the raw material is farmed from animals on a large scale. As the popularity of down garments grows we have an increased responsibility to ensure that our insulation is produced in environments where animal welfare standards are being maintained.

The responsible down standard is an an independent, voluntary global standard that aims to ensure that down is sourced from ducks and geese that have been treated well. This means farming down in environments that allow them to live healthy lives, express innate behaviours and not suffer from fear, pain or distress.

Down fill power

Fill power refers to the quality of down. Fill power does not refer to the amount of down used and it cannot be relied upon to give an idea of a product’s warmth, unless, that is, you are also considering the products 'fill weight' too.

We grade down according to the size of the clusters, that is the amount of air that the down is able to trap relative to its weight.  To do this we take 1 gram of fully lofted down and record its volume, the result represents the down’s “Fill power”.

All of our Duck down is 650FP and our Goose down ranges between 750 and 1000FP. The range of down that we use allows us to fine-tune our garments to meet the differing demands of our customers, both in terms of budget and intended use.

  • We use 650 Fill power duck down in everyday jackets, such as the Axion or Deep Cover Parka where the same volume of goose down would be too warm and in our Asylum bouldering jacket where weight and packability are not a primary concern.
  • 750 fill power goose down is used in our best-selling Microlight and Microlight Alpine jackets as it’s warmth-to-weight ratio is perfect for jackets where the fill weight is low, and packability is of prime concern.
  • 800 Fill power goose down is used in our technical mountain jackets, from the waterproof Valiance to the classic Neutrino Pro.
  • We use 850 fill power down in our Continuum and Infinity-G jacket, designed for alpinists who need to minimise weight. Because of the high levels of loft, these jackets pack down small but still provide enough warmth to make them ideal for high altitudes and low temperatures.
  • We only use 1000 fill power goose down in one jacket, the Zero-G. The Zero-G combines incredibly high quality down with an ultra-fine 7d Pertex® Quantum outer in the ultimate alpine down jacket. Its warmth-to-weight ratio is unsurpassed and it represents the pinnacle of Rab’s down expertise.

Warmth to weight

How warm your Jacket is will depend on a number of factors, but in the main it comes down to fill power and fill weight.  Most lightweight, technically oriented jackets tend to use a very high fill power, however, this doesn’t mean our lightweight jackets are necessarily warmer.  The Asylum jacket uses our lowest grade 650FP duck down yet it is one of the warmest in our range, simply because it contains a lot of down. 

A jacket for everyday use can use a larger quantity of relatively low fill-power down, because weight isn’t a concern and the warmth requirements are modest. In contrast a jacket designed to be carried on climbs in winter conditions must be both light and warm. in this case using a high fill power down lets us put less in the jacket and achieve a higher ratio of warmth to weight.


Down garments are usually constructed using a series of Baffles. Baffles are individual chambers which hold the down in place, ensuring an even distribution of insulation and minimising cold spots. It is these baffles that give many down jackets their distinctive appearance.

We use two types of baffle in the construction of our down jackets, stitch through and box-wall.

  • Stitch Through

In stitch through (or sewn through) garments the baffles are created by stitching the outer fabric directly to the inner fabric. We use stitch through construction in most of our down jackets as it minimizes the amount of outer fabric and stitching required, which provides a significant weight saving. Whilst this is the best construction method for lightweight garments, it does have one drawback. Because the down is pinched at the seams, reducing the space it has to loft, stitch through garments have a less consistent level of insulation than those constructed using box wall baffles.

  • Box Wall

Box-wall garments are made from distinct box-shaped compartments that run horizontally around the body. Because the box-shaped baffles are not pinched at the edges there is space for the down to fully loft throughout the chamber allowing for an even distribution of down and vastly reducing the likelihood of cold spots. The extra material used to create each box means that these garments are usually heavier and less packable. However, in the most extreme temperatures, they are often the best solution.

  • Materials/Fabrics

Without the array of revolutionary Pertex® fabrics that our designers have at their disposal, creating down garments that meet the very different requirements of our customers would be impossible. 

The longstanding relationship between Rab® and Pertex® is key to ensuring that the garments we produce represent the pinnacle of design. Below we outline the Pertex® fabrics that we use in our range.


Pertex® Quantum

Pertex® Quantum is a material with a tightly woven structure which is both light and soft. These properties make it an ideal fit for down clothing as it allows down insulation to fully loft. It is also highly windproof, so the warm air inside your jacket stays there even in high winds. Pertex® quantum also has a durable water repellent (DWR) applied which helps to shed light rain and snow, extending the time before your down starts to absorb moisture.

We use Quantum across our range in a variety of different fabric weights, balancing weight and durability from our classic kinder smock to our ultra-light Infinity-G

Pertex®  Quantum Pro

Pertex® Quantum Pro uses a water resistant coating to provide increased weather resistance. This makes it ideal for jackets that are going to see year-round mountain use, especially when they also feature hydrophobic down.

We use Quantum Pro in our Electron, Axion, Positron and Neutrino Pro jackets.

Pertex Shield

Rab uses Pertex Shield across our range of waterproof jackets. For those down jackets that need to be waterproof as well as warm, Pertex Shield is the outer fabric of choice.

Pertex shield is the outer fabric for our Batura, Resolution and Valiance Jackets.

What about Microlight?

Pertex® have recently changed the naming of their fabrics to simplify their range for customers.

Pertex® classic, Microlight, Quantum and Quantum GL are now simply known as Pertex® Quantum.

Other features to look out for

  • Cuffed waist and wrists

Keeping air trapped around your body is key to the effectiveness of a down jacket. Cuffed waist bands and wrists mean that warm air can’t escape from inside the jacket, so you warm up faster and stay warm for longer.

  • Hood

It’s worth looking for a hood with a wired or polymer peak to help it keep it’s shape in high winds, and consider whether or not you’re likely to wear a helmet underneath. All of our active mountain jackets are designed with helmets in mind.

  • Pockets

Big pockets are great for storing winter gloves and stashing other useful supplies. Our Asylum jacket even includes pockets for your rock shoes.


It’s worth checking that the pockets in your jacket are positioned out of the way of your harness and gear if you’re planning to use it while climbing.

  • Stuff sack (packability)

If you’re not planning to wear your jacket all day it’s worth checking whether it comes with a stuff-sack so that you can attach it to a gear loop or pack it down small enough to fit in your bag. All of our jackets that include a stuff sack have it listed on the product page under specifications.