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Why Down Jackets Keep You So Warm: Down Science Explained

Down Jackets Keep You Warm

A down jacket is often a jacket insulated using the soft and warm under feathers from duck or geese. Down is a superb insulator because loft (or fluffiness) of down produces 1000s of small air pockets that trap warm air and keep hold of heat; thus, it helps keep the person wearing it exceptionally warm in cold winter season weather.

The down fill on the jacket will be either goose down, duck down or perhaps a mix of both. Goose down is most often considered the warmest and lightest but duck down jackets, or jackets which have a mix, tend to be less expensive.

Nearly all major outdoor brands will ethically source this down as a product of the food industry to refrain from cruel practices like live-plucking and force-feeding. If you are unsure, always check with the company.


The Science Behind Down Heat Insulation

Down is used because normal feathers cannot retain loft on their own, which explains why there have to be certain proportions of down to balance a percentage of feathers in any garment classed as a 'down insulator'. This is where the percentage figure you will notice on many down products originates from. To provide an example, where a down jacket uses the percentages 80/20, this shows the item of clothing carries 80% down, and 20% normal feathers.

Down is measured by its "fill power",' also called "loft"- Fill power is how the overall quality of down is measured, and the higher the fill, the better the down. The amount is calculated based on how much space one ounce of down clusters fills in a cylindrical tube. That is a way of measuring the down's fluffiness. More air gets held in down clusters with higher loft, making the down both lighter in weight and warmer. When down is compacted, the fibres' filaments produce small air pockets that hold heat. This process mimics the natural world of animals that need insulation. Using feathers gives down jackets an excellent warm-to-weight ratio, as the jackets are often very lightweight.

Found in the natural world, down is a material that scientific and manufacturing technology cannot improve upon, at least not so far. No human-made material is lighter or capable of trapping as much heat while letting air in and out of its layers. Some newer artificial
fibres come close, but so far, none can produce warmth to weight ratio greater than a 600 grade down.

One drawback of these warm down jackets is how they handle moisture. These jackets (unless specified) are not waterproof. Moisture causes the down to clump, which will hinder the insulating properties and take a long time to dry out. If you're going to hike in heavy rain, it's always wise to take a lightweight waterproof to wear over the down jacket. Progress in down technology has seen the introduction of hydrophobic down (also known as Hydro down) which means that the down is treated afterwards to handle moisture better than standard down; however, I would not recommend down jacket when heavy, and prolonged rain comes.

If you think you would benefit from this outdoor essential, then take a look at our great range of women's down jackets and men's down jackets that we feature on Walk The Land - including top brands such as Rab, Berghaus, North Face and others.

Advantages Of Down Jackets

  • Lightweight
  • Packable
  • Offer superior warmth

Disadvantages Of Down Jackets

  • Not ideal in a downpour (unless the jacket is also waterproof)
  • Can be difficult to clean
  • More expensive


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