reflectix and condensation?

[dakotaross]

And I'm in the south, so potentially, you're in conditions that are more humid in the winter. I'd be interested to hear from someone in CO, etc., and what they're experience is.

However, my guess is that you're talking about 3 nights in lower temps where there may be a dewpoint issue located between the high temperature of the inner layer of the UQ, and the very cold temp outside. I just don't see that happening at 20s, and I do have some experience there. Again, perhaps there is much greater humidity at 20 in the Adirondacks than where I typically go in the southern Appalachians.

[Boston]

However, my guess is that you're talking about 3 nights in lower temps where there may be a dewpoint issue located between the high temperature of the inner layer of the UQ, and the very cold temp outside. I just don't see that happening at 20s, and I do have some experience there. Again, perhaps there is much greater humidity at 20 in the Adirondacks than where I typically go in the southern Appalachians.

A comfortable temperature inside your insulation is what? 75+ degree's? The inner most portion of your sleep system will be that temp if you're comfortable. The temperature through your insulation will lower and lower the farther out you go, until you get to the 20*F outside air. Somewhere in there is the dew point.

The moisture is unavoidable - it comes from your body. A VBL would actually extend the time before the down becomes ineffective, as it blocks moisture. But then you have to deal with a humid sleep environment.

Also, it's important to note that rbinhood made no claim as to HOW LONG it would take the down to become saturated. Based on some responses in the thread though, it sounds like with-in a week the down would loose a large portion of it's effectiveness.

[dakotaross]

A comfortable temperature inside your insulation is what? 75+ degree's? The inner most portion of your sleep system will be that temp if you're comfortable. The temperature through your insulation will lower and lower the farther out you go, until you get to the 20*F outside air. Somewhere in there is the dew point...

Yes, but if you're efficiently getting your heat to the quilt, then there will be a flow of the heat to the cold outside, pushing the heat to all corners of the quilt and to the exterior, where it then meets much colder air and is dissipated. Again, this is my hypothesis... You don't get to the dewpoint until the vapor is pushed outside the exterior.

It becomes problematic when you are overly insulated with clothes or other materials that insulate you - the definition being that they prevent heat transfer. The down of the quilt still insulates regardless, but now you're dealing with a different type of insulation scenario... you've got the airspace of the down insulating from the cold air in the same manner that a beer cooler does, instead of your heat keeping it out to begin with. What makes it work is when there is sufficient heat production from you, and good flow of the heat through the quilt to the outside, preventing the cold air from entering the quilt.

Another hypothesis... overly overstuffed quilts can be overly insulative to the point where they arrest this flow of heat, meaning the cold is not kept out so much by radiating heat and enters the quilt at a deep enough point where there can be a dewpoint issue.

My guess is that there is some of the moisture gathering inside quilts normally, but that it tends to be toward the exterior where changing outside temps (and dewpoints) have more effect and make it easier to evaporate, but still might accumulate over a long hike. Might depend some on hiking habits and whether you're constantly packing up early in the a.m.

[Crowell392]

Wow now my head hurts

[dakotaross]

Wow now my head hurts

A few Golden Monkeys will help!

[Boston]

Yes, but if you're efficiently getting your heat to the quilt, then there will be a flow of the heat to the cold outside, pushing the heat to all corners of the quilt and to the exterior, where it then meets much colder air and is dissipated. Again, this is my hypothesis... You don't get to the dewpoint until the vapor is pushed outside the exterior.

You're going to make me do math, aren't you? I'll try to avoid it for now.

Dew point is dependent on relative humidity. Let's say, best case, there's a relative humidity of 0% in your quilt. For every 10% RH below 100% the dew point drops 3*F from air temp. So in this case if the air temp in your quilt is 75*F then roughly speaking, it only has to contact a surface that's at 45*F to condense into liquid water. This isn't a perfect explanation, but I'm not a dew point expert. The point is dew point in the quilt going to be higher than the outside air temp.

Now to the other point of your hypothesis. I can pretty much guarantee you your body doesn't generate enough heat to keep the outside layer of your insulation at a high temperature (higher than dew point in the quilt). Why? Because heat transfer through your quilt is based mostly on conduction. And since it's a good insulator, it has a low rate of heat transfer. While heat transfer from the quilt to the outside air is convection. And convection is something like 100X more effective at transferring heat. So what heat get's to the outside is almost immediately pulled off by the air. You'd have to be putting off an inhuman amount of heat to maintain that.

Therefore the outside surface of your quilt is going be close to, if not exactly, the same temp as the outside air. That's pretty easy to test too, if you'd like to try and prove me wrong ;-)

[UpMySleeves]

Good read, thanks guys! I currently have a cheap synthetic "sleeping bag DIY" underquilt and will go camping next week in possibly -20°F weather, so I will be adding a CCF blue pad to my kit. This is why I bought a 3 layer hammock, so I can put a pad between the first two layers, and the UQ between the 2nd and 3rd. I am pretty sure this will keep me warmer than just the UQ.

[jwright]

Great thread, one of the best ones I have seen on heat/moisture here.
It is nice to see a meeting of theory, science and observations/practical experience.
Thanks to all who have and continue to contribute, even if it is to disagree.
jason

[Alamosa]

Gosh, I want to write so much more, but I have to work. Just want to say I'm with Shane on this one. Anecdotal evidence of condensation in down is mostly not there, except for a incident here and there.

You really don't need to rely on anecdotal evidence to prove out what the engineers are saying.

• Weigh your quilts
• Go on a multi-day trip where the temperatures never reach 32*
• Don't use a vapor barrier
• Weigh your quilts when you get home before they warm up.

Your quilts will have gained significant water weight. I'm not a big fan of vapor barriers, but on a long trip, it is necessary.

Now for some pure conjecture based on observation. I too prefer not to bundle up in clothes inside my quilts and often find my feet are warmer. I explain it as a combination of:

• Allowing my body heat to escape inside the quilts creates a micro-climate that allows heat to normalize around my body.
• Differences in insulation in different areas based on clothes/jackets/socks causes cold spots in some areas.
• Clothing (especially socks) can become constrictive very easily hindering the bodies ability to circulate heat.

[dakotaross]

I guess I might be the one drinking the Golden Monkeys if I'm getting into a technical argument with an engineer. I'm a banker, I have no business trying to prove an engineer wrong, and that's not really what I'm trying to do. Somewhere in between the technical truth and actual experience is an issue that I would call "mostly insignificant", at least to most of us. However, the technical truth is just that and for that reason, moisture problems do occur, and for those who experience them they are very much significant.

Just seems to me that there is more going on in the relationship of how down insulation keeps you warm than just the retarding of heat transfer, and there's a lot less going on in terms of moisture in the down, at least most of the time. I base that on experience and from what I read in hiking journals and here on HF or WB. When I was a noob, which wasn't all that long ago (even though I'd camped my whole life), in doing the analytical research to determine what I should buy for gear, I was very much interested in the moisture issue and the "down doesn't insulate when wet" mantra that I kept hearing from a lot of folks. I also kept hearing that its not hard to keep down dry, and for that reason, its warmth to weight ratio trumps the moisture issue for most of us. I think its also worthwhile to note that down, for many long distance hikers, is kept in waterproof bags while in the pack during a hike, so its not like its drying out during the day. So there seems to be a dichotomy of truth - conditions should seem to exist whereby down should be getting wet with moisture, and at the same time, it does not appear to be the significant problem that you might be led to think it must be (at least for most of us). Why is that?

I've offered my thoughts, which are not based in technical knowledge. Its probably true that some hikers find themselves consistently in conditions that are conducive to condensation, and for that reason they are proponents of vapor barriers and synthetic insulation. My thoughts are based on what I consider to be normal, 3-season hiking conditions, not something where it would be consistently below freezing. Condensation is spotty in these "normal" conditions, and my thought is that barriers to air flow on the outside, and barriers to down's ability to trap heat on the inside, will ultimately affect the body vapor/dewpoint relationship. How it works otherwise, I'd better leave that up to others.