Down vs Synthetic Insulation When Wet

Jun 8
7 min read

Too Long; Didn't Read (TLDR)

Step 1) Watch the YouTube video below.

https://youtu.be/o2BpakKjGKI?si=g56YfVgcXVD4o7PM

Step 2) Affiliate links to the jackets we tested:

Down Jackets:

Synthetic Jackets:

Introduction

Ahh, the puffy jacket. A longtime staple to the world of lightweight outdoor pursuits where maximizing warmth but minimizing pack space is at a premium.

Collage of vintage outdoor clothing ads with hikers, puffy jackets, and campers in tents on a rocky desert landscape. — Puffys have been integral to outdoorsy folks for decades.

I’ve wanted to do a deep dive into puffy jackets for some time. Specifically, I’ve always wanted to know how much better synthetic insulation performs than down insulation when wet. Let’s find out together.

Read any article on down versus synthetic insulation and you’ll find that down seems to be superior to synthetic in nearly every aspect: warmth, weight, and compressibility. But its alleged Achilles heel is moisture. And this is where the cheaper, heavier, and bulkier synthetic insulation is supposed to shine.

We tested two inexpensive puffy jackets: one with relatively affordable, untreated six hundred and fifty (650) fill goose down and the other with a generic, inexpensive synthetic insulation. Both have a nylon shell. The down jacket does have a hood, I’m just not going to use it during testing.

Initial Testing & Results

First we weighed each jacket dry.

Down Jacket: 321.8g or 11.34oz
Synthetic Jacket: 385.3g or 13.6oz

Next, we measured the loft or thickness of each jacket dry.

Down Jacket: 3.9cm or 1.5in
Synthetic Jacket: 2.9cm or 1.1in

Then, using a thermal manikin and an environmental chamber, we determined each jacket’s thermal performance when dry.

Down Jacket: 1.92 clo
Synthetic Jacket: 1.75 clo

As expected, the dry down jacket is lighter weight, has more loft, and a higher thermal performance than the dry synthetic jacket.

Two puffy jackets, dark blue and rust orange, laid side by side on wood, with comparison text for weight, loft, and clo value. — Superior performance from the down jacket.

Wet Testing & Results

Then it was time to get things wet. In a real world scenario this typically occurs through perspiration (sweating), precipitation (rain/snow/sleet), or plain bad luck (a leaking water bottle in your pack or an unfortunate fall into a stream).

After dunking and thoroughly soaking each jacket, we hand wrung them just like we’d do it out in the field. Then we re-weighed, re-measured, and re-tested both jackets. Lets see how they compare.

Hands wring wet clothes in a clear plastic bin in two close-up photos on a gray wood background. — Soaking the jackets.

First, the weight:

Dry Down Jacket: 321.8g or 11.34oz
Wet Down Jacket: 589.9g or 20.8oz
The down jacked absorbed 268g or 9.46oz of moisture; an 83% absorption rate

Dry Synthetic Jacket: 385.3g or 13.6oz
Wet Synthetic Jacket: 958.3g or 33.8oz
The synthetic jacket absorbed a whopping 573g or 20.2oz of moisture; a 148% absorption rate

Bar chart comparing dry and wet down and synthetic jackets; wet jackets weigh more, with moisture gains labeled in grams and percent. — Water uptake of the two jackets.

Ok, wait…what?! If the synthetic insulation is supposed to be better at retaining heat when wet then why did it absorb and retain more than double the moisture of the down? Put a pin in this; we’ll address it shortly, but let’s continue.

Next, the loft or thickness:

Dry Down Jacket: 3.9cm or 1.5in
Wet Down Jacket 2.1cm or 0.83in
The down experienced a loss of 1.8cm or 0.71in. That’s a loss of 46% of its dry loft, meaning the wet down jacket is only half as thick as when it's dry.
Dry Synthetic Jacket: 2.9cm or 1.1in
Wet Synthetic Jacket: 2.4cm or 0.94in
The synthetic jacket saw only a miniscule loss of 0.5cm or 0.2in. That is only seventeen percent (17%) of its dry loft.

Bar chart comparing loft in down and synthetic jackets dry vs wet: down drops from 3.9cm to 2.1cm, synthetic 2.9cm to 2.4cm. — Loft retention when wet.

So while it absorbed significantly more moisture, the synthetic insulation was able to maintain most of its lofting ability when compared to the down insulation. Let’s see how this shakes out with the thermal manakin.

Line chart comparing heat loss over 6 hours for Synthetic red and Down blue, with arrows showing both recover upward after a dip. — Thermal performance when wet.

Thermal performance:

Both jackets saw an immediate loss of most of their insulative properties. At its lowest, the down jacket retained only 36.5% of its dry thermal resistance. The synthetic jacket, despite its significant water uptake rate, was able to retain 64.6% of its original dry thermal resistance, nearly 30% more than the performance of the down.

The jackets begin a short recovery and quick plateau. This is the drying of the fabric material in direct contact with the manikin’s skin. Once that layer is dry, then begins the slow, steady drying of the insulation layer, expanding outwards with time. Interestingly, both jackets and insulation types recovered at similar rates, despite the fact that the synthetic jacket initially absorbed a lot more moisture than the down jacket did.

I took some images of the manakin in the cold chamber with a thermal camera to visibly see the progress over time. You can see the dark, colder areas and the gradual emergence of warm, bright areas where heat is starting to make its way to the surface of the jackets. You’ll notice that the bottom of the sleeves and torso are the slowest to dry due to gravity pulling the residual moisture downward.

Thermal image comparison of a down jacket and synthetic jacket in two rows, showing bright heat patterns and labels on a wood background — Thermal images of the jackets slowly drying while being worn by the thermal manakin.

I kept each jacket on the manakin for around 6 hours. When I extrapolated the data to estimate how long it would take until each jacket returned to 100% of its dry thermal resistance, the synthetic jacket would take roughly 9 hours compared to the down jacket taking an estimated 11 hours.

Line chart comparing Synthetic (red) and Down (blue) percentages over 11 hours, both dip then rise; red stays higher, with up arrows. — Estimated drying times.

Keep in mind that this time model is only a simulation in a hyper-controlled environment. The manikin generates heat at a constant rate inside of a cold chamber that keeps a constant temperature. A real-world scenario has a lot of varying physiological and environmental factors to consider. This merely demonstrates that the down would likely need hours more time to fully dry compared to the synthetic insulation.

Findings & Conclusion

What surprised me most about the test results was the difference in water uptake. The synthetic insulation retained significantly more water than the down insulation, yet still outperformed the down in terms of warmth and drying time.

I did some reading on past research that was done by the US military on insulation performance and found that they saw similar results. And why is that? Synthetic insulation is typically made of polyester or some other synthetic fiber. These fibers have microscopic pores that trap and hold water, leading to increased water absorption. Down clusters, on the other hand, are composed of quills, filaments, and tiny barbs that don’t absorb water as readily. Down feathers will clump up when wet, but they don’t absorb moisture like synthetic fibers.

Scanned document page with a yellow-highlighted sentence about polyester battings retaining twice as much water as down and feathers. — Article 1

Highlighted book text about polyester batting insulation’s water-repellent properties and down’s moisture resistance on a white page. — Article 2

Which leads us to our ultimate conclusion:

Synthetic insulation does indeed keep you warmer when wet. How much warmer? In our experiment, around 30% more than down. It maintained 64.6% of its thermal performance when wet. And we determined that our synthetic insulation will dry more quickly than the down.

Two puffer jackets, grey and orange, compared side by side on wood; overlay text shows thermal wet performance and drying times. — Wet synthetic insulation was superior in performance and dry time.

So what is going on inside of these jackets to explain our test results?

Insulation in puffy jackets, and sleeping bags for that matter, works by enclosing a layer of insulating material, in this case down clusters or synthetic material, in an outer and inner shell. The insulating material’s purpose and function is to trap air. And why is trapped air such a good insulator? Two reasons: First, air is a poor conductor of heat, meaning it creates a barrier that reduces the transfer of heat from a warm area (your body or skin) to a cold area (the outside environment). This is true for both conductive and radiative heat loss. Second, when air is trapped within a material or between layers, it effectively increases thickness. A thicker barrier creates a longer pathway for heat to move through, which in turn slows down the rate of heat transfer.

Chalkboard diagram on wood wall showing warm and cold area, air pockets, and synthetic layers with arrows and labels, demonstrating how insulation helps keep a person warm in cold weather — How insulation works.

When we soaked our two jackets, both lost some of their thermal performance. But the down insulation lost significantly more. You see, the same characteristics that make down Number 1 in the lightweight and compressibility categories are those that put it at a severe disadvantage when wet. Those weigh-nothing, fluffy, compactable down clusters collapse and smush together when exposed to more than a spritz of moisture. Contrast that with synthetic insulation, known to be heavier, much less compressible, and sometimes just plain bulky.

And therein lies the answer, loft. Insulation loses loft when wet or damp. And some insulation types lose a lot more loft than others. If you recall, when we tested loft, the down jacket lost 46% when wet. The synthetic jacket lost only 17%. That heavier, bulkier, and less compressible synthetic insulation is simply able to better maintain its loft and thickness, and that is the primary reason it can outperform natural down and keep you warm, even when wet.

Person in a blue plaid shirt holds a handful of wet down and a handful of wet synthetic insulation, comparing the two against a wooden backdrop — Down vs Synthetic Insulation When Wet

Discussion & Limitations

First, isn’t natural down intrinsically water repellent? It comes from waterfowl, you know. The answer is yes and no. Yes, down clusters are hydrophilic at the micro level, meaning they don’t absorb moisture like the microscopic pores found in synthetic insulation. But on the macro level, wet down clusters clump together and lose their ability to loft and create air pockets. Waterfowl have much more efficient ways of keeping their down dry than humans do.

Goose preening on calm water with another blurred goose behind; text says Look Up Waterfowl Preening If You Want to Learn More — How waterfowl keep their down dry.

Second, this wasn’t a true side by side test. The down jacket was warmer to begin with. So if my down jacket is so superior initially, doesn't that mean it could be warmer than a synthetic jacket, even if it gets wet? True, and yes. Our intent with this test wasn’t to do a side by side test of these two jackets. Rather, it was to gain some insight on what you could expect from down and synthetic insulated products respectively. But, just for arguments sake, when you look at the real numbers of these two jackets, the down jacket dropped from providing 1.92 clo to 0.7 clo while the synthetic jacket dropped from 1.75 to 1.35 clo. And the down jacket didn’t ever catch up.

Last, what about other types of insulation? DWR down, wool, fleece, etc. Comment below if you’d like to see another round of testing with more insulation types included. We would love to make it happen.

Three outdoor tops on wood background: brown hooded jacket, tan patterned sweater, and coral REI zip hoodie. — Other types of insulation.

Summary

Synthetic insulation has less warmth-to-weight than natural down insulation, and has less packability or compressibility. It also absorbs a lot more moisture when soaked. But its rigid structure allows it to maintain loft and create air pockets even when wet, which results in superior thermal resistance and quicker drying times compared to its down insulated counterparts.

So after this experiment what are we carrying today? Well, a mix. If you can keep them dry, down jackets and quilts are still unmatched. But after this test, I did find this used North Face Thermoball jacket (not sponsored) for use during shoulder seasons and so far, I like it a lot.