Compress sleeping bag in the morning first?
Aug 10, 2017 at 8:20 am #3484148
Hi all, very long time lurker here with a question related to the ever popular topic of maintaining down sleeping bag loft on a long trip.
Occasionally over the years I have seen recommendations to compress your sleeping bag first thing in the morning to push the warm (and humid) air out, before laying it out to further dry – to keep that humidity from condensing in the insulation as the bag cools. Is this a good idea?
I have done this over the years, but have never been confident that it results in less moisture retention. I have wondered if in fact it would be better not to do this? Maybe the residual warm air actually helps drive moisture out of the bag? What do you think?Aug 10, 2017 at 9:43 am #3484171Matt DirksenBPL Member
@namelesswayLocale: Mid Atlantic
Just so I understand you; are you asking if squeezing your sleeping bag out “like a sponge”, then opening it back up again, is a good idea toward helping it dry out?
If so, it sounds like a reasonably decent idea, as long as the bag gets re-lofted again to allow for good air exchange, and not immediately sent to the compression sack. I’d think a good shake or two should do the trick – unless a portion of it is actually wet.
My instinct tells me to always give my down as much air space as practical under “normal circumstances”. So if I normally compress the hell out of my quilt on a trip when my pack is full, I might give it some more breathing room as my consumables get depleted. On nice days, I might squish it into the mesh on the outside of my pack, just to give it some fresh air.Aug 10, 2017 at 10:10 am #3484176
Exactly – essentially roll it / compress it to push out the warm humid air in the bag from you right away on getting up – and re-loft the bag and put it out in the sun to dry – to keep that humid air from you from condensing in the bag’s insulation.
As far as what is best on days where you can’t put the bag out in the sun/wind to dry before packing – I wonder if it is still better to push out the warm humid air, and give it a few shakes to reloft in the shelter before packing.
The real question I am getting at is – does the accumulated warm and humid air from the sleepers body that is in the bag’s insulation first thing in the morning contribute moisture to the bag or does that warm air help drive moisture out?Aug 10, 2017 at 10:57 am #3484181Jeffs ElevenBPL Member
That is the line you toe for max efficiency.Aug 10, 2017 at 11:14 am #3484183Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
If laying the bag out will dry it out, then probably any humid air from sleeping will quickly dissipate even if you just let it sit there
You could try weighing it before and after you squeeze air out?
Squeezing the air out may cause the down to be more compressed which would be worse than any benefit from squeezing humid air out?
I do that with my thermarest mattress, but there’s no air flow with it. But I question whether it makes any difference. I can’t detect any change in weight.Aug 10, 2017 at 11:55 am #3484186
I thought about weighing, but a simple before and after wouldn’t cut it. You would have to weigh it before and after a complete sleep, compress, lay-out, and pack cycle vs another night/morning when you skip the compress part. And because both your metabolism and the weather won’t be the same two nights in a row you end up needing to design an experiment with enough data for a statistical view of the problem. Not really worth the trouble.
And I think you may have hit on why it is better to just get up and leave the bag lofted for a while, warm humid air from the sleeper and all – and weather permitting out in the sun. Compressing it immediately might just ensure that whatever moisture is in the bag is driven into the down clusters.Aug 10, 2017 at 12:00 pm #3484187Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
get up in morning
immediately weigh it
squeeze air out
I’d bet dollars to doughnuts that there will be no measurable difference. But, maybe going through this exercise would lead to some useful idea
perfect experiment for engineer with excess creative energy : )Aug 10, 2017 at 12:18 pm #3484194Kenneth KeatingBPL Member
@kkkeatingLocale: Sacramento, Calif
I’m not sure there’s enough moisture in the air remaining to be able to condensate. And if so, since the air has been basically purged, there’s such little moisture remaining I don’t think it’s going to make a difference.
Most of my hiking is the Sierras with a cuben fiber, single wall tent. Moisture collects on the inside at nighttime and typically gets the foot end of my quilt slightly damp. My hikes typically start before the sun rises, so there’s no time to dry out the quilt. I just stuff the quilt into it’s bag, then into the bottom of the backpack, and when I take it out 12 hours later there’s no more dampness. My thoughts are that the moisture distributes itself evenly throughout the quilt. It’s still there, but not enough to really make a difference. I used to worry about this, but it’s never been an issue so I no longer worry.Aug 10, 2017 at 3:21 pm #3484222Matt DirksenBPL Member
@namelesswayLocale: Mid Atlantic
“The real question I am getting at is – does the accumulated warm and humid air from the sleepers body that is in the bag’s insulation first thing in the morning contribute moisture to the bag or does that warm air help drive moisture out?”
Well, it depends. What air am I waking up to? Cold/dry? cold/humid? hot/dry? or hot/humid?
Here are a couple things to consider:
- Convection transports vapor (moisture) A LOT more efficiently and quickly than through vapor diffusion.
- Air and the surrounding vapor will do whatever it takes to go from hot to cold, and from wet to dry.
- The simple act of me getting out of my bag will most likely replace all of the warm/humid air that was there with whatever air is around me. So we are now only talking about the inside surface temperature of the bag still being warm, and that temperature differential driving vapor to the outside surface of the bag.
- We never want to create a situation where the internal temperature of the insulation hits it’s dew point – if at all possible.
So, if I am in relatively dry air, even cold dry air, there could be more than enough differential between the warm surface of my bag and it’s outside counterpart; to effectively transport all the vapor over time.
BUT, if if the outside air is rather humid, I might run the risk of creating a dew point inside my bag once I’ve gotten out of it, since the inside of the bag’s surface will quickly start cooling off.
Therefore, picking the bag up and shaking it (or rolling it up, then unrolling it), would all help toward moving that vapor along, due to all the lovely convection I am creating.Aug 10, 2017 at 7:26 pm #3484288
Thanks for the comments. I am probably over thinking this.
Jerry – weighing immediately after getting up and then again after pushing air out wouldn’t really answer the question WRT any moisture left behind in the insulation. Now if you had a “dry” weight from the night before that would at least give you an indication if any moisture stayed behind – but still would not tell you whether it is better to push the air out first thing or not. You would need to repeat the experiment, including weighing the night before, without pushing the air our first thing. But then you would also be subject to variations in the weather and you own metabolism on different nights that might swamp the results. And I am an engineer – but running low on creative energy (and I’m a EE anyway) ;-)
Kenneth – I frequently backpack in the Adirondacks where the humidity is often fairly high. In the fall, after a couple days of damp 40 degree rainy weather, with no chance to dry a sleeping bag, then clouds/mist/humidity will hang around all day – again no chance to dry the bag, followed by a high pressure system late in the day, lifting the lid off (no clouds) and night time temps tumble into the low 20s. In this type of scenario packing a damp sleeping bag each night will gradually degrade the insulation – and then when you really need all of those down clusters some of them refuse to report for duty.
Matt – I had not fully considered the impact of the external humidity on this question. Again, I am probably over thinking this and as you say – simply moving around and giving the sleeping bag a shake is enough to get the job done as well as it can be done.
Up until now I had been doing this (pushing the warm/humid air out first thing before airing out), but after pondering this comment from Jerry: “Squeezing the air out may cause the down to be more compressed which would be worse than any benefit from squeezing humid air out?” I am concerned that I may have been making things worse by driving whatever moisture was present into the down clusters. I think I will revise this practice and just give the bag a good shake and then let it air out in the sun (if present) before compressing.
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