Pertex Quantum, condensation and a sleeping bag

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horizon
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Pertex Quantum, condensation and a sleeping bag

Post by horizon »

I've got a Rab Ascent 700 sleeping bag with a Pertex Quantum outer (shell). I have an issue with condensation in the polyester inner of my tent (more on that on another thread perhaps). What I have noticed is that the sleeping bag shell appears to attract a far greater share of the condensation than other objects (e.g. panniers or clothing) in the tent. At first I thought this was because the bag was at greater risk of contacting the tent walls during the night. However, I am now wondering whether the Pertex shell is successfully absorbing less moisture than other items and that this remains on the surface.

Any comments or other experience/ideas gratefully received.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
gloomyandy
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Re: Pertex Quantum, condensation and a sleeping bag

Post by gloomyandy »

Could the greater condensation be because you are in it? Extra heat from you and possibly water vapour as well?
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horizon
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Re: Pertex Quantum, condensation and a sleeping bag

Post by horizon »

This could well be but there is a large amount of condensation in the tent and this would be enough to explain what there is on the bag. I have actually used this combination of bag and tent once before but that was last year and I don't recall many really cold nights after warm days - this year has been a bit different. But I did have the same problem nevertheless.The bag is prone to pick up condensation that has run into the "skirting board" area of the inner tent simply because of rolling around at night and the foot of the bag being in proximity to the end of the inner. I've no doubt that it is I who is producing the condensation (one litre per night apparently) but am baffled as to why the bag gets the worst of it.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
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Re: Pertex Quantum, condensation and a sleeping bag

Post by gloomyandy »

Looks like the Pertex Quantum has a DWR coating on it, so maybe that makes the condensation bead up more and makes it more obvious?

I seem to remember that when I've managed to get water/rain on my PHD sleeping bag (that has a "Drishell" outer that I think may be similar to your Quantum) it has beaded up a lot and I could sort of brush it off.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by Vorpal »

gloomyandy wrote: 22 Jul 2021, 7:22pm Could the greater condensation be because you are in it? Extra heat from you and possibly water vapour as well?
This was my first thought.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by nsew »

It may be a combination of the sleeping bag being too warm for the conditions (excess heat) and the inner tent not being sufficiently breathable. It’s important that inner tents are highly breathable otherwise they form an impenetrable barrier for vapour to escape.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by gloomyandy »

Double post sorry!
Last edited by gloomyandy on 23 Jul 2021, 10:32am, edited 1 time in total.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by gloomyandy »

Condensation is odd I've never been able to figure out when/if I will get it in my Terra-Nova Voyager.

The door (which makes up a large area of the inner tent), is a double mesh and fabric construction so that in hot conditions you can have a pretty large area that is just mesh which helps with ventilation, but the outer fits pretty closely to the ground which limits the air flow. But on most of my trips not having the tent blow away has been more of a concern!

My PHD bag is probably "over hot" at times which probably does not help, but I often get some cold nights on a trip so it's hard to strike a balance. I often used to travel to Scotland in early May, but in more recent years I've tended to end of May, early June and although this usually means I get better weather, condensation is certainly more of an issue.
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horizon
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Re: Pertex Quantum, condensation and a sleeping bag

Post by horizon »

nsew wrote: 23 Jul 2021, 7:39am It may be a combination of the sleeping bag being too warm for the conditions (excess heat) and the inner tent not being sufficiently breathable. It’s important that inner tents are highly breathable otherwise they form an impenetrable barrier for vapour to escape.
I'm less concerned, ironically, at this point about the condensation generally, rather the fact that it seems to take a particular liking to the shell of the sleeping bag. No, the inner tent isn't sufficiently ventilated (I don't always open the mesh vent) but that also implies that the bag isn't too warm (it's about right in fact).

A couple of extra points: I can generally wipe away the condensation and the bag dries very quickly in the morning, even inside the tent. I don't get the impression that the moisture is soaking in. So the bit I am still unsure about is whether the bag (by virtue of its hydrophobic shell) is actually attracting condensation or is, conversely, dealing very effectively with it or a combination of the two.

My next port of call is to comprehensively deal with problem of the condensation but I did want to reassure mysef that I wasn't ruining my sleeping bag in the meantime.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
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Re: Pertex Quantum, condensation and a sleeping bag

Post by simonineaston »

I'm going with the condensation/beading thing. My understanding of condensation is that its a physcial phenomenon, with moisture content and temp. gradient being factors. Thus the large amount of moisture exhaled by your good self over several hours is trapped in the atmosphere of the tent, where it cools and then condenses on the available warm surfaces, the bigger the temp. gradient the more the moisture in the air condenses. The outer skin of the bag is probably often the warmest, largest surface in the tent - and furthermore is made of a material specifically designed to deal with moisture by allowing it to bead on the surface, as opposed to it wicking into the fabric threads... it sounds to me as if alles in ordnung ist, as they say in Germany. :-)
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Re: Pertex Quantum, condensation and a sleeping bag

Post by pjclinch »

horizon wrote: 23 Jul 2021, 10:51am My next port of call is to comprehensively deal with problem of the condensation but I did want to reassure mysef that I wasn't ruining my sleeping bag in the meantime.
To comprehensively deal with the condensation problem, simply we-write the laws of physics to suit yourself!

There, that was easy...

I don't think you have a problem unless the down is getting properly soaked, and often, before packing it, and it sounds like that isn't happening. It's easy to get paranoid about wet down, but if it getting just a bit damp was a deal breaker nobody would have used it in the UK for since synthetic hollow fibre was invented: just make sure it gets a proper air and dry at the end of the trip before long-term packing.

Back to the condensation thing, if you're out in atmospheric conditions where a dew is going to form you'll quite possibly get some in your tent (it'll probably be a bit warmer inside, so not so much as is liberally coating every blade of grass in the vicinity, but still some all the same). When there's a dew the air is full of moisture and as the temperature falls overnight the relative humidity goes up until it gets to 100% and then the water in the air has to go somewhere. Any amount of vents, mesh, open doors, closed doors, Miracle fabrics or clever flysheet cuts aren't going to change that, even if they can help moving some of the damp away.

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Re: Pertex Quantum, condensation and a sleeping bag

Post by PH »

simonineaston wrote: 23 Jul 2021, 11:44am Thus the large amount of moisture exhaled by your good self over several hours is trapped in the atmosphere of the tent, where it cools and then condenses on the available warm surfaces, the bigger the temp. gradient the more the moisture in the air condenses.
I wouldn't bet on it - But my understanding was that condensation occurs when warm air meets a cooler surface.
If that's correct, it makes no sense that the warm air is condensing on the warmer bag more than any other surface, I suspect something else is happening.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by thirdcrank »

I thought the point already made was that something else isn't happening: the Pertex isn't absorbing the condensation and so it's a lot more obvious.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by horizon »

PH wrote: 23 Jul 2021, 12:03pm
simonineaston wrote: 23 Jul 2021, 11:44am Thus the large amount of moisture exhaled by your good self over several hours is trapped in the atmosphere of the tent, where it cools and then condenses on the available warm surfaces, the bigger the temp. gradient the more the moisture in the air condenses.
I wouldn't bet on it - But my understanding was that condensation occurs when warm air meets a cooler surface.
If that's correct, it makes no sense that the warm air is condensing on the warmer bag more than any other surface, I suspect something else is happening.
I find the Pertex to be a cold, shiny material - it isn't even IMV a very attractive material for a cosy sleeping bag but if it does the job (lightweight, water resistant, down resistant etc), that's fine by me. The polyester inner tent was definitely getting a hit, as was the floor, but clothing wasn't. I now wonder if:

1. The Pertex is "colder" enough to attract more condensation - it appears so - but then deals with it better (i.e.doesn't absorb it so easily).
2. Other fabrics (warmer, softer) don't attract so much condensation but are absorbing it more easily. I have no way of knowing at this stage whether articles of clothing etc were actually damper than the sleeping bag by the end of the night.

As you can imagine, it's pretty difficult to be completely scientific about this - every night the weather conditions were different, including one night at 8 degrees (yes, you did read that correctly).
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
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horizon
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Re: Pertex Quantum, condensation and a sleeping bag

Post by horizon »

simonineaston wrote: 23 Jul 2021, 11:44am . . . and furthermore is made of a material specifically designed to deal with moisture by allowing it to bead on the surface, as opposed to it wicking into the fabric threads... it sounds to me as if alles in ordnung ist, as they say in Germany. :-)
Yes, I think this is my (very hesitant) conclusion too. Quantum isn't the most hydrophobic Pertex fabric available - they tell us that Pertex Endurance is better in that respect.- but it must be pretty good.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
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