What’s the benefit of synthetic?

Advertising for years comes up claiming that "synthetic is now as good ad Down".

If you saw microscopic pictures of good fluffy down, and similar pictures of synthetic insulation, you would tend to believe that the wonderful structure of down developed by millions of years of evolution isn't easily matched by humans squirting resin through little extrusion nozzles.

However, it is likely to be true that real inexpensive down can be beat on a loft per weight by the very best of the synthetics.

Confused? Thank marketing and their desire to mold your mind to get the dollars out of your wallet.

Ryan, I think you have the down / synthetic pluses and minuses covered (assuming we are talking about high quality down):

Down
+ higher warmth-to-weight ratio
+ lighter
+ compresses well
+ loft has longer lifetime
– expensive
– not good when wet

Synthetics
+ cheaper
+ safer when wet
– lower warmth-to-weight ratio
– heavier
– doesn't compress as much as down
– loft degrades earlier than down

I think BPL's philosophy to go with synthetic vs down has important merits.

First, synthetic is safer than down in wet conditions.

Second, by viewing both your clothing and sleeping bag (quilt) as your sleep system – i.e. supplementing a synthetic quilt with synthetic clothing – you can kind of have your cake an eat it to. You have the safety of synthetic in inclement conditions and a light weight system because your clothing is duel purpose: part of a sleep system and used around camp.

Personally I have a mix of both down and synthetic. I use a down bag and synthetic clothing.

My decision on a down bag was one of loft longevity and weight-to-warmth.

My decision on synthetic clothing was one of cost and a margin of safety in the unlikely event my down bag gets wet.

Ryan:

The only thing confusing is advertisers' irresponsible claim that today's synthetics have approached down in terms of warmth and compressibility. It's a fiction — and thus no confusion at all.

Use synthetics when moisture is a significant threat. Otherwise, down is still the more efficient insulation.

Both the comments about the marketing of Synthetics vs. Down and the inherent superiority of down are correct. However, you should spend some time tracking down as much of the ongoing discussion of these two insulation technologies as you can so you can make up your own mind.

If you are likely to be out for an extended period of time in cold conditions where you will not have sufficient time to air out and/or expose a down bag to the sun, then the down bag will accumulate moisture which will degrade its insulative properties. Hence the use of synthetic insulation under these conditions. But if your use a vapor barrier to line the bag, this would not be a problem and you would then be back to using down.

Do you see the problem in a one comment solution to this issue?

Both down and synthetics have their place in the outdoors. It takes a knowledgeable backpacker to know when to use each. Become knowledgeable.

> "New synthetic insulations, escecially Climashield, are the lightweighter's dream" (posted on another thread) and seeing that BMW's entire Cocoon line is synthetic.

>The only benefit I'm aware of is that wet down does no good, and synthetic is safer in this regard.

…I'm the one who posted that. As Roger said, you've pretty much summed it up. The reason why synthetics are a lightweighter's dream is that they allow you to wear/bring as much as *all* of your daytime clothing to bed if you want to/have to. And they allow you to do it every night, even if you're damp after the day. That includes your damp base layers, your soaked socks, and your jacket that has absorbed a bunch of sweat during a rest break. By morning, your body heat will generally have dried your duds and you can carry on. Many people choose synthetic insulation because some or all of that moisture may wind up in your sleeping bag/quilt.

The issue is the condensation point. Your body heat will drive vapor from your skin (and damp clothes) outwards through your layers of insulation. At some point, though, this water vapour will cool down enough to condense, and become liquid water droplets.

If the vapour makes it all the way out through your base layer, jacket, sleeping quilt, and bivy *before* it condenses, life is good. You are drying your sleep system with body heat, and there's no concern.

What commonly happens, however, is that cool and/or damp ambient conditions experienced at night will make that vapour condense *before* it has exited your sleep system. This Condensation Point (aka Dew Point) may be located *inside* of your bivy, or it may even be inside of your sleeping quilt. This is a frequent occurrence, especially in climates like the Pacific Northwest and New England, and especially during the shoulder seasons.

If this condensation happens in or on synthetic insulation, no-harm-no-foul. It may feel clammy, but it will still keep you almost as warm while you wait for morning. If, however, you use down insulation? You are in for a difficult night. Your down will start to gain weight and collapse, and will very quickly become into a sloppy mess. Once it's a wet sloppy mess, it holds *no* heat and you might have to start thinking about getting a fire going. (Hopefully it's not raining or snowing. :)

"Well I am careful to keep all of my clothes and gear dry."

So is almost everyone. But as a lightweight backpacker, you probably have fewer options to help you do this. You probably don't have an extra jacket, or a full change of clothes to wear to bed.

Also, your skin gives off moisture all night long. This is called Insensible Perspiration, and it's a process whereby your skin tries to maintain a certain minimum humidity on its' surface. Your wicking base layers are constantly taking this humidity *away* from your skin, and your skin is constantly perspiring at a low level to replace this lost moisture. If it's cold/damp enough, all of that moisture winds up in your insulation. (More than a pint a night, apparently.) Some Arctic explorers report sleeping bags weighing 60lbs by the end of their trip because insensible perspiration has been freezing in the insulation for weeks or months: it's a real and potentially dangerous phenomenon depending on your circumstances.

Since the dew point is generally not *immediately* next to your skin, some people have success wearing down insulating gear inside of a synthetic bag. That way you have synthetic insulation at the condensation point and down where the moisture is not likely to condense. This same down layer, however, will likely be worn during the day — not practical on rainy+humid expeditions!

There's also the issue of external moisture. The shelters involved in lightweight backpacking are often more prone to condensation than the big double-walled tents of traditional backpacking. If it's cool and rainy outside, this can lead to sleeping in a home-made fogbank all night. Some users have reported actually watching a down sleeping bag collapse over the course of a night.

Finally, many lightweighters are involved in more remote/extreme trekking. A fall in the river, a leaking platypus, or a down bag that becomes soaked during a day or two of humid/rainy camping is no big deal when you're 10 miles from the car. But imagine being 100 or more miles from civilization, at 2 a.m., possibly solo, with a failed insulation system and a bad case of the shivers. Such a scenario is why many experienced lightweight backpackers opt for synthetic insulation pieces over down ones.

I disagree with the below statement. Please review human physiology of sweating. The princeton article online was wrong too and that is why the CDC (it was on their site too) made them take that part out.

The body DOES NOT sweat to maintain a certain humidity percent on the skin surface. Insensible perspiration is an involuntary diffusion of water molecules through the skin due to normal metabolism and is not controlled or stopped by outside influences including vapor barriers.

Outdoor books that many put faith in have wrong information on this aspect of human physiology. Some of the information has been perpetuated since the 60's or 70's from perspiration medical articles that never proved what those books still state to this day.

================
Brian James said,
This is called Insensible Perspiration, and it's a process whereby your skin tries to maintain a certain minimum humidity on its' surface. Your wicking base layers are constantly taking this humidity *away* from your skin, and your skin is constantly perspiring at a low level to replace this lost moisture.

Matt,
Who's post is wrong?

Umm I don't really have a response. I thought I'd read most of that on BPL.

It seems counterintuitive to me, though, that moisture wouldn't evaporate from my skin.

After all, anything that has free water molecules on it, including skin, is subject to evaporation. How is it that skin is exempt from this law of physics?

Also, how is it that Will Steger's sleeping bags got so heavy on his way to the North Pole? It certainly wasn't raining, and airborne humidity at -40 is quite low. How did his sleeping bag gain 35 pounds, if not from moisture coming off his skin?

Perhaps some manufacturers of VBLs would benefit from this revelation as well; they could immediately stop selling a product that apparently has no benefit.

i dunno matt, ive been writing research papers lately and it has been my experience that in order to have a legitimate argument, whether you are right or wrong, some sources need to be cited more than 'the CDC said so' and maybe contain more of an argument than 'thats all flat wrong'.

Despite all of the science behind perspiring, i find synthetics superior to down for me. My 12 oz 40* XP quilt packs to 3 liters, my 26 oz 20* primaloft quilt packs to about 6 liters, both very small. My 14 oz thermawrap parka packs to about 2L as well. Differences with down are negligible in both weight and size until you get into 4 season. Syn is cheap, easy to make and modify, and I have no reason to carry a bivy (6 oz at least). I do believe that advances in sleep gear design can lead to 20* syn bags that are as light as 21 oz with a small zipper and hood. That compares to pretty much every down bag of similar temps. Synthetics are almost there, but have a little more work to do before they reach total warmth/weight with 800 fill down. The other benefits i believe outweigh the difference already.

Concerning getting stuff wet at night with sweat, i try to stay very close to the limits of my sleep gear because I hate sleeping hot and it just doesn't feel right waking up cozy and warm on the trail. sadly, sometimes i carry too much sleep gear for the temps and I sleep like most people like to- warm. I have a hunch that whenever someone is 'properly' prepared for the weather they encounter, they will sleep warmly. sounds pretty good. i also think that when you are warmer than you need to be, your body perspires to cool you off. i hypothesize that this may be the cause of the wetness in peoples bags at night. The north pole fella may have either been sweating a bit at night because he was warm and prepared, or he wets the bed at night and didn't tell anyone. just my 2 cents

Brian wrote:

> It seems counterintuitive to me, though, that moisture wouldn't evaporate from my skin.
> After all, anything that has free water molecules on it, including skin, is subject to evaporation. How is it that skin is exempt from this law of physics?

Very good question, and the answers are important for us.

There are substances called 'poly-alcohols' which have some quite amazing properties. One is that they can be spread out extremely thin yet remain a continuous film. Another is that they are fairly opaque to water transport. So if you took a cupful of a suitable poly-alcohol and poured it onto a dam, it would spread right across the surface of the dam and block all evaporation. Quite amazing. Of course, a bit of wind and a few ripples and the film would be broken, but never mind.

Left to the forces of the environment, your skin would dry out amazingly quickly and become most unhealthy. A bit like sun-dried meat. It avoids this by generating its own poly-alcohols – aka skin grease, and this thin layer stops surface evaporation from your skin. So cool skin does not evaporate very much at all.

When your body needs to pump out heat for cooling it opens up pores on the surface and these pores allow direct evaporation. This is sweating. Sometimes the amount of moisture being pumped out exceeds the surface evaporation capacity and free moisture results: wet sweat, drips on the face, etc.

The surface evaporation capacity can be exceeded when the air surrounding your skin becomes saturated. Hot still days are good for this. On the other hand, a good breeze will strip the humidity away from the surface of your body, allowing better cooling.

So a cool dry body which has NOT been freshly washed may lose very little moisture while asleep. On the other hand, soap and water will remove this skin grease and let you sweat more easily. But note that lots of salt on the surface of your skin may upset the poly-alcohol layer. For this reason it makes sense to rinse your skin in the evening to remove sweat salts, but don't use any soap or you will remove the valuable protective skin grease layer.

Cheers

Thanks for the info, Roger. The "that's all flat wrong" guy seemed to be suggesting that the humidity next to our skin was not relevant to the amount of moisture lost to a sleep system, and/or that none of the skin's moisture migrates to your sleep system during the night. Or something…actually he didn't really say anything, so I had to infer these statements by inferentially parsing his ambiguous negativity.

I don't doubt that the skin is well adapted to inhibit unwanted moisture loss. Otherwise we'd all (being 96% water or whatever) look like dried apricots and have to drink 10 gallons of water a day. You Aussies would have to just connect your veins directly to the kitchen taps!

Poly-alcohols or no, though, I still believe that everybody (every body) loses water through their skin into their sleep system. Particularly if (as you mentioned) there's some salt on your skin from the day, and particularly if 98% of your skin's poly-alcohol-excreting surface area is being constantly rubbed and scrubbed by a freshly washed piece of polypropylene or wool.

This is why a VBL adds such an amazing amount of warmth to a sleep system, despite being an inherently noninsulative item: it's only function is to stop moisture transport, and stopping moisture transport alone makes a substantial difference in your ability to stay warm.

That's what I was trying to convey with my post.

Brian

The hotter it is the more you sweat. Some people sweat more than others. You always sweat unless you are freezing to death. It is all relative. I would love to be able to take along a lighter weight down bag but… Lugging along a household dryer is out of the question. On many a night I went to bed in my synthetic sleeping bag with damp clothes and the extra damp socks circulating around in the sleeping bag. The next morning PRESTO! Everything dry and I could have filled my water bottle with the condensation on the inside of the tent (MSR Zoid)! If it's windy and I can set up the tent with the foot to the wind that problem disappears too.

I agree that a synthetic bag is a wonderful clothes dryer and I use one for climbing for that purpose. I also agree that a synthetic bag might negate the need for a bag cover/bivy under a tarp or in a condensation filled tent.

However, after using PG Delta, 3D, and Primaloft, I have yet to find a synthetic that keep sme as warm as good down (all things being equal).

For instance, I like my DAS Parka for a belay jacket, but when it is cold (between 10-20) and I am standing around belaying, I have yetto be really warm. In fact, my MH Phantom down jacket keeps me warmer- even with no hood and a waist length cut… I have noticed this with bags as well.

My solution is to use a lightweight down jacket and a synthetic bag in the hopes that the bag will dry any moisture in the jacket during the night. After a weeklong trip in the Cascades last spring (very wet and constant ice or snow), I noticed no loss of loft in my down jacket (Phantom). I slept in it inside a 20 degree TNF Delta PG bag (what is that one called?).

I have an old down jacket but would like to upgrade to a much lighter synthetic option. I like to canoe and kayak, so synthetic seems like a better choice there, plus in a survival situation I would think I would be less likely to wet out a synthetic jacket in snow/rain if I was injured and/or just lost.

But I found this BPL article on the subject to be interesting about the relative drying time of down vs. synthetic:

http://www.backpackinglight.com/cgi-bin/backpackinglight/wet_weather_performance_down_vs_synth_vests.html

"surprise discovery – the down Flash vest recovered loft as quickly as the synthetic Micropuff and after 30 minutes of drying its loft exceeded the Micropuff's."

I will say in my experience of washing and drying a down bag and a polarguard bag, the PG bag is much less wet and clumped after washing, and dries much faster to me.

I interpreted that article to conclude that only extremely thin, lightweight vests resulted in similar drying charateristics. I don't believe that they intended to infer that the same results would apply to thick sleeping bags, using down vs sythetic insulations.

Personally, I use synthetics for clothing that is exposed on the trail to the elements (sweat, rain and wet vegetation) and I use a down sleeping bag since I have the protection of my tent. I also, don't do long distance hikes. Mine are limited to 2-4 days.

Loft recovery in little vests on active people is a different animal than loft recovery in a 2" thick quilt on a sleeping person.

Once your down is soaked, it will take a *huge* amount of heat energy to convert all that water into vapour and restore the loft of your down. And extra heat energy is something a sleeping person doesn't have. (Hence the need for a sleeping quilt in the first place.)

We seem to have two different threads in one here; unless you consider the overlap of sensible perspiration affecting down more than synthetics.

Anyway, the following acronym I use might help some new members realize the factors involved in insulation choices. Expereienced members already know this.
I choose insulation based on METTT; the
Mission (fast and light, car camping, etc)
Exposure (water, snow, ice, humidity, tarp or enclosed tent, etc.)
Terrain (fuel-less alpine or forest, etc..)
Team members (all carrying down!?), and
Time (long damp durations favor synthetics)

So a week on the Olympic coast results in a different combo than a weekend on a dry mountain top. And if one person is carrying all down you might want to carry a synth as a backup. With UL backpacking your insultation is a system; for example a jacket would be worn when active, and to boost the insulation properties of a lightweight bag.
Personally I favor a synthentic MB Thermawarap set in a light down bag.

Has anyone here been really wet in a synthetic bag? I have and I can tell you that I didn't notice much in the way of thermal properties. While synthetics (and excuse me here cause I ain't much of a scientist) may be a bit more tolerant of wet conditions, in really wet conditions neither one is "safe" to be in. Just pointing out that "safer" is a pretty relative statement in this case and shouldn't give a false confidence in synthetics.

Yes, soaked, but you can ring synthetics out (not too harshly though), which helps their thermal efficiency a lot. It gives a bit of a cushion in a worst case scenario.

I think the susceptibility of down in wet conditions is vastly overstated. Down has some natural water resistence, if you get the surface of your bag/clothing wet it will dry without much trouble. Surface meaning not thru-and-thru wet. Also a good water resisitent shell goes a long way.
The only advantage of synthetics besides cost is the abillity to ring and sqeeze the water out.
If your bag is soaked to the core like that than you had to have done something really, really stupid.

I think it's understated.

Last winter I changed my dry body into dry clothes, laid down in my dry down bag in my dry well-ventilated tent, and drifted off remembering that it was humid so I'd have to wake up and check for condensation.

In the middle of the night, a cloud drifted into my tent. I had proper low-high ventilation arranged and I was ready for humidity. But I could actually see the wisps of cloud/fog moving around the tent and drifting in the vents.

If I'd closed the tent up any more, I would have been in a condensation bubble.

By morning, my down bag was like a sack of wet leaves. Whereas it was previously at its' maximum compression in its' stuff sack, it now took up *half* the stuff sack.

I was camping on 15' of snow, and there was wet snow falling. There was no *way* I could have dried it out. I thanked the deities that I was just on a gear-testing overnighter, strapped on my snowshoes, and got the heck out of there.

As stated, if it had been synthetic I would have at least had a fighting chance. But if your METTT involves humidity that hovers just above or just below freezing, you could reach the failure point of your down despite doing everything right.

Synthetic just has a more extreme failure point in terms of humidity/moisture saturation. Also, it's possible to bring it back from the dead using body heat.

I don't know much about making clothes, but it was my understanding that synthetic gear could be made without a "shim", thus making the construction (not counting the fill) lighter. I think the Cocoon gear used to make a claim based on that idea (something like "for this weight, it is actually warmer than down"). Of course, even if you gain a little in construction, you would lose it once you started adding more insulation. In other words, a very thin synthetic might be warmer than a down jacket of the same weight, but once the jacket gets thick, the down is lot warmer. I've noticed that the Cocoon gear is no longer sold with this claim. This makes me wonder if the original claim was unfounded or the jackets are heavier (thus making a down jacket of the same weight warmer).

Brian,

What does the addition of a bivy do for a situation like the one you just described? What about when you are under a tarp?

I too slept on 15' of snow at the base of Mt. St. Helens one winter with my 7 year old. Night time temperatures dropped to 18F with daytime temps peaking around 42. We were in clouds by nightfall. As we were protected by trees, there was not much wind through the night in our 4 season double-walled tent. I had with me a down Marmot Lithium sleeping bag rated at 0F.

I woke up the next morning with puddles on the top of my bag, no visible loss of loft and from the waist down, the top of the bag was covered in ice. I remember feeling cozy, but not hot. There is no doubt I let out a lot of water that night. Mostly from exhaling I am sure.

My 7 year olds bag was a 15F REI Zigzag. It kept her toasty with a synthetic base layer she wore that night. She had no dampness on her bag anywhere.

As far as perspiration goes, I have to agree that one perspires a lot through the night, at least based on how hard they worked to get there. The efforts involved may crank up your metabolism causing more sweating than the next guy with a 15 pound pack.

Just my .02c

P.S. I will say based on that experience alone, I would not trust down for more than a weekend at best with the conditions we were in.