Condensation issues Enlightened Equipment quilt

One possible explanation…

Did both bags have similar loft?  If your friends bag had more loft it is possible that it experienced the same amount of condensation, it just happened *inside* the bag.

Actually I noticed the same thing this August on a 13 day trip along the northern half of the JMT.

I have a 2012 EE quilt, rated at 20 degrees.  This is the OLD design, the one that had the square kero-step baffles.  My wife has a brand new EE quilt, rated to 10.  We sleep in a TarpTent Stratospire 2 with the partially solid inner.

On several occasions during that trip, we woke up to find that her quilt was damp on top while mine was dry.   She asked me why this was happening.  I couldn’t give her any explanation.    We sleep on the same sleeping pads (Nemo Tensor Insulated on top of an 1/8″ Gossamer Gear pad), and as I recall, the vestibule doors were set up the same on both sides each night.

There is a difference in loft between the two quilts.  The fabrics on these quilts are obviously different, as EE has probably switched to lighter and different fabrics since 2012.

When folks started replacing their single pane windows with highly insulated ones, complaints started flowing in claiming that the new windows were forming exterior condensation on them while the old windows did not. People thought there was something wrong going on. While the physics of this particular phenomenon are well understood (when the dew point is at or very close to the air temp, then condensation will form on any surface which is a a similar temperature, but will always be much more noticeable on surfaces which can’t absorb it (like glass & metal in particular). The old single pane windows didn’t have this problem, because they had a measurably higher outside surface temperature on the glass (due to it’s inefficiency) and allowed so much more heat to radiate out of them. So when condensation was forming all over other objects outside, the windows appeared fine.

This applies to sleeping bags as well. And the bag material (and it’s dwr finish) will also  be an attributing factor to this. So the colder the outside surface of the bag, the more likely condensation will form.

But I personally believe there is another thing that might be an issue, and this may have to do with bags that are noticeably more vapor permeable: “capillary condensation”. In my experience, EE bags are quite breathable (compared many other quilts), and will easily allow vapor and even air to pass through them. As far as I’m concerned, this is a GOOD Thing. But given the warm/humid to cold/humid exchange going on, it’s entirely possible to get condensation on surfaces where the RH is less than 100%. The first third of the following article has a very good description of this phenomenon: https://www.buildingscience.com/documents/building-science-insights/bsi-099-its-all-relative

What has worked very well with me is to put my quilt inside of a silk mummy liner (I cut small slits in the sides of the liner so I can still strap my quilt to my pad, and sleep over top of the bottom of the liner between me and my pad. It nudges the temp rating up just a little bit, reduces the probability of drafts,  and acts as a sacrificial layer to absorb the condensation that WILL form. But because it gets quickly wicked away and absorbed by the liner, the bag remains quite dry. Yeah it added 140g to my kit, but it’s well worth it.

Thanks for all this information! I might consider a liner, at least when there’s a chance conditions might be particularly conducive to heavy condensation and concerns about wetting through are high. Those are the kind of conditions when I probably wouldn’t mind having a somewhat warmer setup anyway.

I was thinking sort of what Matt said

single pane window – less insulation value – outside is warmer so any condensation evaporates

quilt with less insulation value – outside is warmer so any condensation evaporates

maybe your EE quilt has more insulation value so the outside of the quilt is cooler so it evaporates condensation less so it accumulates on the outside

just brainstorming here, I don’t know that there’s a solution here – use a quilt that has less insulation value?  that doesn’t seem like a good idea

I have noticed that the outside of my quilt will sometimes get condensation on it early in the night but by morning it’s dried off

there is a skin of air over the quilt that adds some insulation value.  the outside surface of the quilt can be 10 degrees warmer than the surrounding air.  If the relative humidity outside is 100%, the relative humidity right at the outside surface will be somewhat less because it’s a little warmer.  That means any condensation will evaporate and drift away more.

where does the water that’s condensing on the outside of your quilt come from?  if it’s from your body, then a vapor barrier liner would help.  vapor barrier around your body would keep any water from evaporating and moving out through the quilt.  just as an experiment, you could wear a base layer, then a garbage sack with holes for your arms and head.  most of the sweat from your body is from your torso.

you breath out a lot more water vapor than you sweat.  Are you breathing into the quilt?  If you do that it’s really tough to deal with all the water vapor.  I wouldn’t think this would end up on the outside of your quilt though, it’s normally a problem with a bivy and there’s condensation on the inner surface of the bivy.

maybe the condensation on the outside of quilt comes from humidity in the air.  when I cowboy camp, and it’s clear, because of radiative heat loss the outside of my quilt will be 10 degrees cooler.  This often causes condensation on the outside surface of the quilt.  This is what’s happening with grass and brush and stuff, it will accumulate a huge amount of condensation on a clear night.  But, you’re inside a tent so this won’t happen, it would just be on the outside surface of the tent.  The tent material will absorb any radiation from your quilt.

maybe at least one idea here that would inspire something useful?

Friend of mine takes groups of kids from his school out winter camping. The most popular activity is building a quinzee and sleeping out overnight. Humidity in there can be horrendous and along with condensation on the walls there is a very good chance of getting the sleeping bags wet.

He asked to sew some bivy bags with a waterproof base but a highly breathable upper, aim is to move the dew point out from the surface of the bag. In this case the condensation sits as ice on the fabric of the bivy bag. I used an uncalendered 1.6 ripstop, for the top, extending the waterproof base up the head and foot ends. Feed back so far is positive, the kids bring the damp bivy back to base ( often a heated tent) in the morning to be dried out.

(persuaded my wife to model the first one, big enough for -30 sleeping bag and pad)

I guess this something like your silk over bag? Maybe making something in a sub 1oz nylon would be an option and leave out the zipper.

Have you emailed EE and ask them about this issue?

Here’s what I got from EE today:

Condensation, for the most part, is a product of external conditions. Air is high in humidity, the surface of the bag is cold, and the moisture in the air condenses out. If your friends do not have the same condensation problem, it would make an interesting physics problem to see why not. Maybe your bag is more insulated so the surface is cooler than the others, so more moisture condenses out.

Some moisture also comes from inside the bag, however. You give off several pints of water vapor at night, and that can also condense on the surface this is know as insensible perspiration. Maybe you just give off more moisture than your friend. It’s really hard to say because there are so many variable in the equation. Individuals produce more or less vapor. different fabrics, DWR, insulation will all play a roll in this. The water vapor given off by your body will condense when it reaches something whose temperature is at, or below, the dew point. It has nothing to do with surfaces, per se. Condensation occurs on a surface only if that surface is below the dew point, and everything the water vapor has encountered previously is not. If the temperature is cold enough for the dew point to be within the down of your sleeping bag (as it may well be in winter or with your friends sleeping bag), then that is where moisture your body gives off will condense (dampening the down). Otherwise, the condensation will occur further out, on the shell of your quilt or sleeping bag. Now the moisture cold be condensing inside your friends sleeping bag, which may not be noticeable. It’s hard to say. I guess the real question is, were you cold or warm vs your friends experience? That can tell us a lot. If you you were warm and slept well then it performed how it should have.

Moisture, or condensation does not harm down at all, in can impair its ability to be thermally efficient, making it not as warm as it could theoretically be. But it will cause no long term harm if it dries properly.

As to how to alleviate this, it’s hard to say exactly with out trial and error, and in many conditions it is unavoidable, depending on temperature, humidity, and dew point, and an individuals sensible or insensible perspiration. Warm air transitioning towards cool air will always cause moisture to condense at the dew point. Ideally, if you have proper insulation that is out side of the quilt. If the quilt isn’t quite warm enough that can happen internally, and that can be a problem. Sometimes changing your baselayer can matter as some manage moisture better than others. Venting in a tent our shelter can play a critical role as well, and help minimize this. Ultimately a Moisture Vapor Barrier between the individual and the quilt or sleeping bag can solve this problem. But this is usually only used in scenarios well below 0°, but that is exactly its purpose. Dampness, can be deadly in sub zero conditions, and mountaineers try to minimize this as much as possible.

How good is the DWR treatment on the exterior of the quilt?  If a few drops of water do not bead off the exterior, it has very little water repellence, and unlike your friend’s commercially made bag, will more readily absorb moisture in the air.  Note that the less ventilation in the tent, the greater the moisture content in the air.

Another possibility is that rather than water repellent, the fabric has a treatment that makes it somewhat water resistant, or less ‘breathable’.  This is not unusual, and has been a cheap way of water repellent or DWR treatment.  If so, it would collect more condensation on the fabric’s inner layer from vapor from your body; but because the fabric is not HIGHLY water resistant, or waterproof, some of the moisture would seep through into the outer fabric surface.

Either possibility suggests a fabric that is not well suited for the outer shell of a sleeping quilt or bag because it is not both highly water repellent.and highly breathable.

Granted, the late Jack Stephenson promoted bags that were highly water resistant on the inner shell, and even sold water resistant liners.  Some people liked this approach, as it was said to lower perspiration in the bag.   Not for me, thanks.