Down insulation vs synthetic insulation: Which is best?

Not all insulated jackets are created equally and one of the first steps to choosing the right jacket for you is understanding the different types of insulation available.

Insulated jackets typically fall into one of either two categories, “down fill” which are natural fibres taken from the underside of a duck or goose, or “synthetic” which features man-made, polyester fibres packed tightly together.

No one type of insulation is necessarily better than the other and choosing the right type for you will depend on the task at hand. This article will help explore some of the key structural and performative differences between down fill and synthetic insulation in order to help you pack the right jacket for your next expedition. 

What’s the difference between down and synthetic insulation?

You’d be forgiven for thinking that “down” and “feathers” are the same thing - but this is not strictly true.

“Down” refers to the loftiest fibres found beneath the feathers on a bird, normally taken from the breast area where they keep the bird’s vital organs warm.

Owing to their natural structure, down fibres are highly breathable, they’re hydrophobic (meaning they repel water), and their loft helps trap and store heat generated by the body. In terms of practicalities, the structure of down also makes it highly compressible which makes for jackets that can more easily pack down.

Melee Jacket | Down Insulation

However, down insulation inevitably has a saturation point. Too much water ingress and the down will clump, losing its loft and its ability to insulate as a result. This might not be an issue if you’re heading somewhere cold and dry, but something to bear in mind if it could get wet/humid on your travels.

Given the difficulties posed by down fill and wet weather/humidity, “synthetic” insulation was designed to mimic the qualities of down whilst retaining heat even when wet.

Synthetic insulation is made up of polyester fibres intertwined with a mix of filaments in differing sizes to create a lofted structure. In a similar way to down, these lofted structures, made up of all these ultra fine fibres, help trap heat in the air pockets between them in order to keep you warm. Unlike down fill, the structure and composition of synthetic insulation means it doesn’t lose any loft when wet. This will help you to stay warm even in humid or showery conditions. Not only that but synthetic insulation dries quickly as well.

Ithax Jacket | Synthetic Insulation

But - this technology comes at a price as synthetic insulation has a lesser warmth to weight ratio than down. This means that you need more of it to achieve the same level of insulation, in practicality this can make for heavier, less compressible insulated jackets. 

Which type of insulation is best?

So which type of insulation do you need? We’ve summarised the pros and cons below.


Down Insulation


  1. Dry, cold climates

  2. Expeditions requiring low carry weight

  3. Stationary/slower paced pursuits at lower risk of sweat buildup


  1. High warmth to weight ratio

  2. More compressible and easy to pack down


  1. Loses insulation when wet

  2. Dries slowly



Synthetic Insulation


  1. Wet, cold climates

  2. Expeditions where carry weight is less of a concern

  3. More dynamic pursuits where sweat management is crucial


  1. Will not lose insulation when wet

  2. Dries quickly

  3. More affordable alternative to down


  1. Heavier and less compressible than down

Which insulated jacket is right for me?

The primary thing to consider is whether you will be using the insulated jacket in cold/dry or cold/wet conditions as this will influence whether you opt for down or synthetic insulation.

You will then need to think about what temperature you will be using the jacket in - for the most extreme conditions you will want a high fill power (over 550+). In milder climes, a lighter jacket with a lower fill power may be more appropriate.

It is worth bearing in mind the packability of your jacket. Depending on the task at hand you may need to pack a lighter insulated jacket that stuffs down well into a daysack, for more short term or stationary pursuits you will likely get away with a heavier jacket that isn’t required to pack down.

None of these considerations should be made in isolation and the process is less a step by step one than an evaluation in the round. When preparing for an expedition you should be balancing the ideas of wetness, temperature and carry burden - depending on your particular pursuit you may need to compromise on one over the other.

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