Down Vs. Synthetic Jackets

Of all the various categories of outdoor outerwear —from hardshell jackets to softshell pants to fleece midlayers— insulated jackets are the most complex, nuanced, and specialized. A half a century ago explorers, hunters, outdoorsmen, and climbers used heavy wool layers and down jackets to keep warm. Today, technology has advanced to include multiple blends of synthetic insulation and a range of fill power down variations, all in a variety of fill weights and face fabrics. Insulated jackets now encompass everything from ultralight, packable down midlayers to heavy, down expedition parkas, and are specialized for a variety of weather conditions, activities or to limit pack weight. Navigating the myriad insulation choices available on the market today can be tricky and confusing, which is why we here at the Outdoor Gear Exchange/ have devised this guide to the ins-and-outs of insulation!

Types of Insulation: Down, Synthetic and Blends


An image of a down insulated jacket from The North Face

Down is a natural insulation material that comes primarily from geese. Goose down, which is a layer close to the skin of the bird, is very high in loft and occurs in large clusters. Down is the lightest form of insulation, packs down much smaller than synthetics, traps air efficiently, and has the highest warmth to weight ratio. In high consequence cold-weather sports like high altitude mountaineering, down is the only option. Consider the following regarding down insulation:


  • Lightest option
  • Most compressible and packable
  • Warmest option (best warmth to weight ratio)


  • Down loses its loft and insulating properties when wet
  • Dries slowly
  • Expensive

Fill Power

Fill power is the number on every down product that measures the loft of the down and can range from 450 to 900. This number represents the number of cubic inches (in3) that can be compressed into a one-ounce volume.  The higher the number the more compressible and lighter the down clusters are when compared to an equal amount of lower quality down. Additionally, higher fill power down clusters can trap more air, which makes them warmer per ounce. Many high-end jackets feature fill power numbers of 700-900, which means that they are lightweight and highly compressible.

A common mistake when examining down products is to assume that a higher fill power down jacket is automatically warmer than one with a lower fill power. This is incorrect. The warmth of a down jacket is also related to fill weight. Therefore, a jacket like the 800 fill Mountain Hardwear Ghost Whisperer jacket with 79 grams of insulation, while incredibly light and packable, will never be warmer than a jacket like the 650 fill Rab Ascent parka with 330 grams of down insulation. However, if you compare an 800 fill jacket with a 550 fill jacket, each with 60 grams of down insulation, the 800 fill jacket will retain heat better and therefore be a bit warmer. Consider fill power primarily for weight and compressibility and fill weight to determine warmth.

Fill Weight

Fill weight is the initial specification to consider when determining how warm a jacket is. The fill weight is the measurement in grams of all of the insulation in a jacket. This measurement clearly signifies how puffy and warm a particular down jacket is. Generally, a down sweater style jacket, which is intended for use as a midlayer or active outer layer will have between 60 and 100 grams of insulation.  A larger belay parka or cold weather climbing jacket will have 250 to 350 grams, while an expedition-style jacket for high altitude and polar conditions will have 400+ grams of down fill. The difference in size and warmth between jackets in separate fill weight categories is obvious, so once you know how you are going to use your down jacket, narrow your search by fill weight.

Hydrophobic Down

Hydrophobic down is a relatively new technology that aims to improve the wet weather performance of down products. Brands like Rab and Mountain Hardwear, as well as sleeping bag manufacturers like Sierra Designs, Sea to Summit, and Big Agnes, utilize hydrophobic down treatment in many of their high-end products. Dry-treated down resists water better, retains significantly more loft and dries much faster than untreated down. While synthetic products are still ideal for very wet weather, down products are closing the gap with hydrophobic treatments. In climates with high humidity or damp conditions where moisture would normally slowly dampen and hinder down jackets and bags over the course of a few days, hydrophobic down products will remain viable for longer and perform better than their predecessors.

Ideal Uses for Down Jackets

  • Hiking, climbing, mountaineering, and skiing in cold, dry conditions
  • Layering under a hardshell
  • Activities and trips where weight and space savings are paramount considerations


A photo of an Arc'teryx Atom LT hoody

If you want to avoid the care and potential downfalls of down insulation, a synthetic fill insulated jacket will suit your needs. Synthetic insulation is comprised of fluffy clusters of fine polyester fibers that trap warm air and insulate in a similar manner to down. Compared to down, synthetics are durable, moisture-resistant, and versatile. Unlike down, synthetics come in different blends and performance is different depending on the brand or design of the material. Here are some features of synthetic insulation to consider.


  • Water repellent
  • Quick-drying
  • Warm when wet
  • Cheaper than down
  • Durable


  • Heavier than down
  • Not as warm per ounce as down
  • Not as compressible and packable

Variations Between Synthetics

While goose down feathers are theoretically the same from brand to brand, synthetics are very different. Jackets with the same fill weights of Primaloft Black, ThermalQ Elite and Polartec Alpha will all have slightly different warmths and heat retention properties. Insulation manufacturers do not release measurements of warmth for their synthetics, but higher end insulations like Primaloft Gold, Coreloft and ThermalQ Elite will offer performance similar to 500 to 650 fill down. If you opt for a more expensive synthetic jacket with a higher grade insulation, you will be significantly warmer than you would be with an inferior blend. Just as down with various fill power ratings will be more or less compressible and feature different warmth to weight ratios, synthetics vary along the same metrics.

Synthetic Fill Weight

Like down insulation, fill weight is an important factor to consider when choosing a synthetic jacket. Like down, synthetic jackets come in multiple fill weights to fulfill different roles. Many insulated sweater style jackets, like the Arc'teryx Atom LT, Mountain Hardwear Thermostatic, and Black Diamond Access Hoody each contain 40 to 60 grams of synthetic insulation, while belay jackets like the Mountain Hardwear B'Layman have between 100 and 250 grams. Usually, brands try to avoid putting large amounts of synthetic insulation —like in a down summit parka— into a jacket due to the weight and bulk that come with that design. Since synthetic jackets are particularly beneficial in high output activities, cold and wet weather, and activities, like belaying, where durability is a consideration; light and medium weight varieties are the most common styles of synthetic insulated jackets.

Breathable Synthetic Insulated Jackets

Recently, outdoor apparel manufacturers have been adopting breathable synthetic insulations that are ideal for high output activities like mountaineering, climbing, or ski touring. These breathable synthetic jackets are warm when stationary, yet breathe well, release excess heat, and dry quickly while active. Jackets with Polartec Alpha like the Rab Strata Hoody are superb temperature regulators and breathe well while still maintaining core warmth. Additionally, Some companies have incorporated breathable fleece or softshell panels into insulated jackets in order to provide added breathability.

Ideal Uses for Synthetic Insulated Jackets

  • Wet, damp or humid conditions
  • Activities where durability is an important factor
  • If you want a jacket that requires less delicate care
  • High output activities where you may sweat in the jacket

So, which will you choose to keep warm this winter?