Eiderdown isn’t just the lightest, warmest, rarest down on Earth. It’s also the only down that’s sourced as a by-product of an entirely natural moulting process. It begins with the eider duck, a seabird native to the icy waters of northern Europe. Each spring, female eider ducks return to land to breed and nest. The layer of down that keeps them warm in the water is such a powerful insulator that it doesn’t allow their body heat to escape. So to keep their eggs warm they moult from their underbellies, exposing a small bald area known as a brood patch. Once the feathers have come loose the ducks have no further need for them.

The down is collected from the eider ducks’ nests by experienced eider caretakers. They relocate close to the nesting ground during May and pick up the feathers by hand after the ducks have shed them. Our eiderdown is collected by Àrni Örvarsson, a third generation caretaker whose family has looked after the ducks for nearly 80 years. It takes 65 man hours, and 66 nesting ducks, to generate a single kilo of eiderdown.

Every gram of eiderdown inside the jacket comes from a small area of land called Hraun, in the remote Fljót Valley in Iceland’s northernmost extremes. Hraun, which translates to ‘lava’ in English, sits between two fjords known as the Troll Peninsula, and is home to a wild sanctuary of some 3,500 nesting eider ducks that have evolved to thrive in this harsh environment. They are capable of diving 60 metres into Iceland’s freezing waters to retrieve mussels, clams and other shellfish thanks to their soft layer of under feathers that keep them insulated from the brutal arctic conditions.

Eiderdown’s incredible water repellency isn’t just the result of millions of years of evolution. It’s also thanks to a uniquely low-intervention cleaning process that allows the down to retain its natural hydrophobic qualities. That’s why it’s guaranteed to keep you warm, even when it gets wet.

Eiderdown is superior to all other types of down because it’s evolved to survive one of the harshest environments on Earth. A look under a microscope reveals a sprawling network of fibres covered in tiny hooks that latch onto each other. This creates a cohesive mass that traps tiny pockets of warm air and gives eiderdown its unbeatable warmth and lightness.

Eiderdown acts like a living organism to keep you warm, responding intelligently to the environment it finds itself in. Inside the jacket it expands to make more warm air pockets in the cold, and contracts when it’s warm to keep you cooler. It’s been shown to be 40% more durable than standard down – as it can be compressed again and again, and will keep returning to shape. And it’s why eiderdown duvets are often passed down as heirlooms in Iceland.

If you ever have the opportunity to plunge your hand into a clump of eiderdown, it's a surreal experience. It’s so astonishingly soft and warm that it doesn't really feel like anything else on Earth. And that makes talking about the numbers feel slightly arbitrary. On fill power – a standard measurement for the warmth of down – eiderdown is between 760 and 850, which is high, but not the highest. But when you test for CLO value – which tells you how much a material insulates – eiderdown has been shown to be even warmer than 1000 fill power goose down, which is the warmest you can find. So it's not just a better insulator gram for gram than goose down. It's less bulky, too.

The eiderdown is protected by an ultra lightweight Nylon shell. It’s so lightweight that it’s almost translucent, so you can make out the natural colour variation of the eiderdown underneath. It’s windproof, downproof and treated with a water repellent coating, so that light rain and snow roll off its surface.

The yarn we use to make the outer shell is incredibly fine and lightweight. The weight and thickness of the material is defined with a unit of measurement called a ‘denier,’ which works by weighing 9000 metres of a single thread to get a measurement. For example, 9000 metres of silk weighs 1 gram, so silk is 1 denier (1D). An average human hair is around 20D. It’s rare to see materials lighter than 10 denier even in high performance outdoor gear. But the Eiderdown Winter Puffer’s outer shell is made from 7 denier Nylon.

You’ll find two side pockets on the outside of the jacket, both of which put your hands underneath the eiderdown for warmth. There’s a third zipped pocket inside on the left chest, and a two-way zipper runs down the centre of the jacket. At the hem you’ll find an elasticated cord adjuster, while the cuffs come with a clean elasticated finish.