Pertex Quantum, condensation and a sleeping bag

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thirdcrank
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Re: Pertex Quantum, condensation and a sleeping bag

Post by thirdcrank »

The Pertex is "colder" enough to attract more condensation
To attract extra condensation, something has to be truly colder, ie at a lower temperature. The fact that a fabric such as Pertex may feel colder than, say, fleece says little about the temperature of either.
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horizon
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Re: Pertex Quantum, condensation and a sleeping bag

Post by horizon »

pjclinch wrote: 23 Jul 2021, 11:46am

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.

Pete.
This is starting to look like a consensus of opinion which is very reassuring. :)
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 »

thirdcrank wrote: 23 Jul 2021, 1:01pm
The Pertex is "colder" enough to attract more condensation
To attract extra condensation, something has to be truly colder, ie at a lower temperature. The fact that a fabric such as Pertex may feel colder than, say, fleece says little about the temperature of either.
This is where I am in the hands of the Gods and why I have sought advice from our good forum - I simply don't really know what is happening here. Someone might be along in a minute to explain the difference between different fabrics to the extent that they attract more or less condensation and whether, as you say, they can be colder or not or whether this is purely subjective.

PS Just to add, Pertex Quantum has a "durable water repellent" finish which may explain things.
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
thirdcrank
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Re: Pertex Quantum, condensation and a sleeping bag

Post by thirdcrank »

Imagine your Pertex outer was instead made from the same material as rubber gloves it would in these circumstances be dripping wet because it would be just about impermeable: any condensation would be obvious because it couldn't be absorbed. However, anything inanimate and not decomposing will normally be at the same temperature as its surroundings. Anything warmer or colder is being or has recently been, heated or chilled in one way or another. Somebody mentioned above bathroom taps. There's usually no condensation on the hot tap because of the hot water. If you had two unfitted taps they would normally feel cold to the touch but they would be at the same temperature as their surroundings unless that had just changed.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by mattheus »

FWIW I'm agreeing that the coldest surface will attract the most condensation - the skin of your bag MUST be warmer than the tent. Unless you're dead.

Meanwhile: why do people want a waterproof bag if you're inside a tent? Isn't breathability/wicking the bigger priority (after warmth, that is!)
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horizon
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Re: Pertex Quantum, condensation and a sleeping bag

Post by horizon »

This is from Quora but it doesn't say whether thermal conductivity would increase condensation or not:
Although things made up of different materials are preserved under same temperature conditions in the same room, they may feel relatively warmer or colder than the other materials.

This can be explained by the effect of a material-specific parameter called Thermal conductivity. How well a material conducts heat is called Thermal conductivity. Steel has a greater thermal conductivity co-efficient and hence conducts heat very well. Wood has a lower thermal conductivity co-efficient and blocks the flow of heat. Let's say you're in a room maintained at a temperature of 20 Degree Celsius (68 Fahrenheit) and your body is at a normal body temperature of 37 Degree Celsius (98.6 Fahrenheit). Assuming, steel and room are in thermal equilibrium with each other, when you touch the steel, heat flows quickly from the warm skin to the highly conductive steel. Your skin rapidly cools off and feels cold. When you touch wood, the wood doesn't conduct heat very well and blocks the flow of heat. Your skin doesn't cool off rapidly and doesn't feel cold.
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 mattheus »

euurgh. "cool off".
What's wrong with "cool" - perfectly, good, clear, english verb.
thirdcrank
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Re: Pertex Quantum, condensation and a sleeping bag

Post by thirdcrank »

horizon wrote: 23 Jul 2021, 1:24pm This is from Quora but it doesn't say whether thermal conductivity would increase condensation or not:
Although things made up of different materials are preserved under same temperature conditions in the same room, they may feel relatively warmer or colder than the other materials.

This can be explained by the effect of a material-specific parameter called Thermal conductivity. How well a material conducts heat is called Thermal conductivity. Steel has a greater thermal conductivity co-efficient and hence conducts heat very well. Wood has a lower thermal conductivity co-efficient and blocks the flow of heat. Let's say you're in a room maintained at a temperature of 20 Degree Celsius (68 Fahrenheit) and your body is at a normal body temperature of 37 Degree Celsius (98.6 Fahrenheit). Assuming, steel and room are in thermal equilibrium with each other, when you touch the steel, heat flows quickly from the warm skin to the highly conductive steel. Your skin rapidly cools off and feels cold. When you touch wood, the wood doesn't conduct heat very well and blocks the flow of heat. Your skin doesn't cool off rapidly and doesn't feel cold.
AIUI, that explains why some things eg metal feel colder to the touch than others eg wood. They are better insulators or conductors but it says nothing about their temperature as measured by a thermometer. If anything, your sleeping bag + accoutrements, will be warmer in use than other fabrics in the tent because your body is heating it. It would be nonsense to suggest that being warmer made it more liable to condensation. On the subject of moisture in down, weigh your sleeping bag after a period of use then give it a good tumble dry; you may be surprised how much lighter it will then be.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by nsew »

horizon wrote: 23 Jul 2021, 10:51am
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.
It’s July, the sleeping bag weighs in at 1.3kg with a comfort range of -2deg to -7deg. Rab describe the bag as being “perfect for the likes of cold bivis and Scottish winter”. It may be 8deg outside but inside your tent its several degrees warmer especially so as you’ll be generating so much heat from that bag. If on top of that the inner doesn’t breathe well (cheap fabric?) you’ve created a highly uncomfortable moisture heavy environment.
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Tigerbiten
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Re: Pertex Quantum, condensation and a sleeping bag

Post by Tigerbiten »

This is what I think may be happening.
The air inside the sleeping bag is warmer than the air in the tent so holds more water vapour.
As you move around in your sleep, this air passes through the outer shell of the bag from the down and hits the colder air, this extra water vapour condenses out on the hydrophobic shell.
Hence the water on the outside of the bag.
It's a bit like camping in ultra cold weather when the water vapour can condense straight into ice either on or inside the bag.

Luck ........... :D
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Re: Pertex Quantum, condensation and a sleeping bag

Post by Vorpal »

I guess you know that condensation occurs from your breath adding moisture to the atmosphere... I can see a couple of possible ways that this is transferring to the sleeping bag (besides that mentioned: it is more likely to come into contact with the walls of the tent).

First, a question... are you using a mattress or insulator under the sleeping bag?

If not, the most likely answer is that the sleeping bag is being kept cool by proximity to the ground, and therefore collects condensation.

Otherwise that explanation must be in how quickly the tent warms in the morning.

Insulation, like in your sleeping bag, reduces thermal conductivity.

During the period when things are cooling down in the evening, this helps you keep warm & reduces condensation.

During the period when things are warming up in the morning, this could mean that the surface of your sleeping bag warms more slowly than the stuff around. Because this surface is (slightly) cooler, that is where condensation occurs.

The conditions must be such that it warms very quickly in the morning, otherwise, a warm body in the sleeping bag should normally prevent that sort of condensation.

Of course, if you have a condensation problem in the tent, it may be hard to discern one aspect of the problem from another.

Condensation can be a problem, especially in the mountains, because there can be fairly extreme differences between day and night during the summer.
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horizon
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Re: Pertex Quantum, condensation and a sleeping bag

Post by horizon »

mattheus wrote: 23 Jul 2021, 1:22pm
Meanwhile: why do people want a waterproof bag if you're inside a tent? Isn't breathability/wicking the bigger priority (after warmth, that is!)
/camping_novice
It's an interesting point (amongst many on this thread). I think Rab and the others are a bit paranoid about getting down bags wet. They probably rightly cannot trust their customers to be vigilant and in any case, accidents do happen - the bag could arrive at the campsite already wet from water ingress in the pannier - it isn't an indoor environment that the bag is used in. Even the feathers these days are treated to resist water. It may be that this is the most water repellent sleeping bag I have owned; it is certainly the first on which I have noticed condensation (note emphasis).
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
thirdcrank
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Re: Pertex Quantum, condensation and a sleeping bag

Post by thirdcrank »

a bit paranoid about getting down bags wet.
Then the obvious thing would be an impermeable liner - then you would know the origing of most of the condensation.
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Re: Pertex Quantum, condensation and a sleeping bag

Post by pjclinch »

mattheus wrote: 23 Jul 2021, 1:22pm
Meanwhile: why do people want a waterproof bag if you're inside a tent? Isn't breathability/wicking the bigger priority (after warmth, that is!)
/camping_novice
First up, there's a clear difference between waterproof and water resistant. You can get waterproof sleeping bags, but they're rather niche items and very expensive. Most people needing waterproofing will use a waterproof cover like e.g. the Alpkit Hunka.

So being clear we're in the realm of water resistant here, one might want it because you're a bit paranoid and/or the place you're using it is prone to drips, spills etc. (see also: hydrophobic down treatments). Even a plain Pertex (or similar fine low denier synthetic) shell is pretty good at seeing off drips, be they condensation forming directly, coming off something else, drink spills etc., so for a lot of the UK market it's more about paranoia than need. Also, paranoia sells! My bags are ME ones with a "Drilite" shell, and while I wanted the winter one with a just-in-case shell, I got it on the summer one because that range left me no choice...
There's also the factor of consequence of failure. If I get a bag soaked on a spring-autumn UK road based cycle tour odds on the worst case scenario is a cold, uncomfortable sleepless night. If, on the other hand, I'm snow-holing for a few days backcountry ski touring in Norway, miles from anywhere and any phone signal, things look a bit different.

I've not found breathability of lightly proofed shells a problem unless I'm also using them inside a cover when there's sometimes clear damp spots around the edges of the baffles. I suspect that's an indication that (as you suggest) you can have too much of a good thing with waterproofing, and I only use a cover if I feel I really need one (I'm sleeping outside and there's a good chance of rain, or sleeping at the bag's limits and I want all the layers I can get). So on the "it's never done me any harm" front I do lean a bit towards a resistant shell, but the fact is in over 40 years of using down bags I've only had one soaking bag disaster and that was a pretty extreme situation camped high in a sleety blizzard where the only reason we hadn't abandoned was our pals hadn't returned from a winter climb and we needed to see if they got back by morning to decide to call out Mountain Rescue.

On the premise that your tent should be waterproof... well, yes, but even if it stays up you can end up touching condensation covered walls, and in conditions where it rains for days it's actually really hard to keep things dry. It gets easier with a bigger tent and experience, but especially over a few days it's really hard to keep stuff dry in a lightweight tent, because any time you go outside you get soaked, and then you go back in... This point means that the longer your trip, the better idea a resistant shell is, just in case the rain sets in.

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Re: Pertex Quantum, condensation and a sleeping bag

Post by pjclinch »

thirdcrank wrote: 23 Jul 2021, 3:00pm
a bit paranoid about getting down bags wet.
Then the obvious thing would be an impermeable liner - then you would know the origing of most of the condensation.
Sold as "vapour barrier liners", and it's a feature, not a bug, designed for seriously cold sleeping. The idea is that otherwise the moisture in the baffles will freeze during the day, which is Not Good, so you stop it ever getting there.

I once saw a grim film of a Russian ski expedition to the North Pole where the first thing they did every day after setting up camp was break apart the icy balls in their sleeping bags. I don't think much fun was being had...

I've never come across anyone using them in the UK.

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