Condensation

[Christopher R]

1. Are there any particular ways to prevent condensation build up under your sleeping pad?

2. Do you generally get condensation in your tent during 45 degree nights, with 65% humidity?  This seems warm to me for condensation build up, but I understand temperature is not the only factor.

I did a test and set up a new tent in my back yard, admittedly on wet grass, and got a bunch of condensation build up under my sleeping pad, and on my  sleeping bag.  Tent vents were open.

3. I am concerned because I plan to soon be camping in wet conditions on nights that are between 25-45, and I am a bit unsure how to keep my tent and gear dry, or dry-ish if its cold and raining outside over multiple days.  It seems that even if I manage to keep dry from the rain, condensation will get me. any advice?

4. Also any tips on packing my tent to keep the inner floor dry when I can’t dry out the outer floor or the fly?

A lot of questions, but any tips would help.  On all my prior backpacking I have never had to deal with condensation, but I think it is going to be an issue in cold-ish rainy weather.

[Matt]

I would not be surprised to get condensation on the tent’s inside walls, or even on my sleeping bag, in the conditions you describe.  But do I read your post correctly in that the condensation also was on the inside of your tent floor (as opposed to the underneath side)?  That would be a new one for me.

Ventilation is the the only real remedy you have.  To maximize its benefits, pitch your tent in places that might catch a slight breeze, keep doors as wide open as possible, and avoid inherently damp areas (creeks, lakes, open fields, and yes, wet grass).

If you do have to pack up a wet tent, I’m afraid I’ve never discovered a way to segregate the dry sections from the wet sections.  Once everything is folded up and packed away, the moisture seems to migrate everywhere.  My solution is to pull the tent out as soon as the sun reappears for a quick, if not exactly compete, drying.

I know none of these solutions provides a silver bullet for your problem.  Moisture is like aging – you can take small steps to mitigate it, but you’ll never defeat it.

[dirtbag]

What tent are u using?

[Matt Dirksen]

“1. Are there any particular ways to prevent condensation build up under your sleeping pad?”

Having lived, camped and hiked in the Mid-Atlantic for most of my life, I am very used to waking up having to deal with something wet. Especially in the winter and shoulder seasons, condensation is a fairly normal occurrence around here – regardless of site location, tent selection, sleeping pad, quilt, so on and so forth. Therefore, anticipating and tending to wet gear is just as important as preventing crucial gear from getting wet. In other words, I always bring a decent sized towel.

But to specifically address your question, the times I have personally experienced condensation under my sleeping pad, I believe there are three contributing factors:

1) the surface temperature of the underside of my pad

2) the temp and relative humidity of the surrounding air I am sleeping in

3) just how cold and saturated the soil is underneath my tent

The worst case of “wet pad syndrome” I ever had was camping on a few inches of snow when both the ground and air temp was well above freezing, and I was in a cozy double walled tent where it was even warmer still. I had enough ventilation inside the tent to keep the walls and my quilt from condensing, the underside of my ccf pad was totally saturated. To me, it was obvious that there was enough moisture in the which wouldn’t condense in 45 degree air, but the temperature on the surface of my tent floor was obviously much colder. Furthermore, I was sleeping on an X-Lite at the time sandwiched by two 1/8″ ccf pads. While the combined R value was fairly reasonable, I still believe there was a reasonable amount of heat radiating from underneath of me.

I believe the contrast between the tent’s floor temperature and the surface temp from the underside of my pad created the condensation.

The good news for me was being able to separate the bottom ccf pad from the rest of my stuff, wipe it down, and keep it separate from then on.

[Greg Mihalik]

Try a piece of new, undamaged watetproof vaporproof plastic under your pad to determine the source of the moisture.

My WAG is moist air moving up through the floor.  But ….. that’s why you test.

[Bonzo]

Maybe it’s just cool, wet air inside the tent sinking to the lower levels and then condensing in the warm areas under the pad.  I don’t experience it a lot for one reason or another, unless it’s really humid and then everything is damp.

[Christopher R]

@dirtbaghiker Slingfin Portal

 

[Christopher R]

@mhr yes, on the inside of the tent floor, under my sleeping pad only.  The rest of the floor is dry, and the net is also dry.  The fly is wet, but nothing dripped through the net

[Rex Sanders]

Backpacking on the foggy, damp parts of the California coast, I’ll echo what Matt said.

Plan on using wet gear and dealing with it. Large-enough synthetic pack towels are definitely worth the weight. Some people bring small sponges.

Wipe everything down as best you can before you pack up in the morning. Then wipe it all down again when you unpack that night, because the remaining moisture migrates everywhere. Some nights I’ve had to wipe down every few hours. Especially if condensation is dripping off poorly designed overhead fabric panels right into my face :-(

Depending on your tent floor waterproofness or hydraulic head (HH), moisture most definitely can come up from the ground through the fabric. But there are plenty of other ways for condensation go get into things.

A lightweight polycro footprint just slightly smaller than your tent outline (no sticking out and catching rain!) can help. Since polycro has almost infinite HH except for pinholes, anything heavier won’t make much difference.

Lots of tent floors advertise seemingly high HH, but HH numbers are easy to inflate. And “1,500 mm is waterproof” pretty much only applies to overhead tarps and tent flies under almost no pressure. For floors that you kneel on and sleep on, you need 10-40 times higher HH to prevent moisture from getting in (let the flame wars begin without me).

That’s why so many tent makers recommend, and just happen to sell, footprints. Less waterproof floor fabric is lighter, but you need a footprint. Interesting business model. Also, most fabric coatings get even less waterproof over time for many reasons.

ALWAYS throughly dry a shelter soon after you get home. Storing wet tents dramatically shortens their life. Most other gear, too.

Independent fabric tester and BPL member Steve Seeber had more to say in this interview:
https://backpackinglight.com/standards-watch-steve-seeber-interview/

— Rex

PS – If condensation wets the surface of your high-quality down quilt or sleeping bag, it will still be warm enough, unless you do something really stupid. Just wipe it off as above. More in a BPL story to be published eventually.

[Dan]

The physics of condensation is not terribly complicated, but the bottom line is that it’s not really plausible to eliminate it completely under all conditions with the type of gear most of us prefer to use. The good news is that, as suggested above, a little condensation is not such a big deal. You will learn to live with it. And frankly, if the only condensation is under your pad, it seems completely benign and irrelevant. In other words, who cares? It’s much worse when you are getting condensation on the inner walls of your tent, but even that is usually tolerable. If you have a break in the weather during the day, take a break and dry out your gear in the sun. Good excuse for a rest.  ;-)

[Matt Dirksen]

“yes, on the inside of the tent floor, under my sleeping pad only.  The rest of the floor is dry, and the net is also dry.  The fly is wet, but nothing dripped through the net”

1) did you have a ground cloth under the tent?

2) how much sleeping insulation did you have under you?

3) how did you take your temperature/RH measurements? (inside the tent or outside?)

Regarding tent floors allowing bulk water to pass right through them. Sure it can and does happen to just about everything, I suppose. I just can’t imagine a Slingfin Portal to be “vintage” enough for this phenomenon to happen, with or without a groundsheet.

I’d start to imagine the can of cold soda on a hot summer day. Obviously the soda is not leaking through the can when this form of condensation occurs but there is certainly enough moisture in the surrounding air to create the condensation.

The air in your tent was probably more than saturated enough to condense when the warm underside of your sleeping pad was in direct contact with the cold tent floor. If you were using more insulation between yourself and the ground, I suspect this would never have happened.

[Christopher R]

@namelessway I was contemplating going without a ground sheet to save weight, so I was not using one, on wet grass.  I think the minimal weight of a polycro tent sheet will be worth it.

My temp measurement was just from weather.com.  outside temp in my city.  Not super accurate.

I don’t think the portal tent floor leaked.  I’ve tested it for leaks, none.  I’m thinking definitely condensation.

Thanks for the info and tips.  Looks like the hitchhikers guide to the galaxy was correct. “A towel is just about the most massively useful thing an interstellar hitchhiker can carry. Partly because it has great practical value.”

[Roger Caffin]

Condensation under your mat is entirely NORMAL when camping on snow.
You are emitting moisture vapour, and the floor or groundsheet is at -5 C. What do you expect?
In the same way, low temps above 0 C will also cause condensation.
Extrapolate.

Cheers
PS: wet grass is also a huge source for water vapour and then condensation.

[Greg Mihalik]

^^^

From the OP –

” … under my sleeping pad only. The rest of the floor is dry …. ”

So the OP’s moisture vapors are preferentially migrating under the matt and condensing, but not condensing on the colder bare floor?

 

[Roger Caffin]

Yeah, very common.
You see, the silnylon under the mat is pressed hard against the cold ground or snow, while the rest is not. With grass, the groundsheet may be quote a few millimetres above the real ground level.

In other words, the rest of the groundsheet is not colder.

In addition, the groundsheet under the mat is probably lower than the rest: water flows downhill.

Cheers

[Rex Sanders]

“I don’t think the portal tent floor leaked. I’ve tested it for leaks, none. I’m thinking definitely condensation.”

To hack a terrible 1990s quote: It depends on what the meaning of the word ‘leak’ is.

Bulk, visible water movement through fabric without visible holes – not what you are experiencing.

Nearly invisible water movement, primarily vapor, possibly through microscopic breaks in the “waterproofing” layer as the layer wears and the nylon fabric weave shifts and stretches, aided by the added pressure of knees and hips and elbows and whatnot – possibly.

And then that nearly invisible water migrating up from below gets trapped under your sleeping mat, insulated from your body heat, and decides to take a long rest on your nice cold tent floor in the form of visible condensation.

Even tents with Slingfin’s reputation will condense/leak/get wet inside under the right conditions. Shocking!

Others here offered plausible explanations. Bottom line: dealing with condensation inside a tent is nearly inevitable and mostly not that hard.

Tent design including wise fabric choices, proper tent care, lightweight groundsheets, good site selection, and opening doors & vents as much as possible, can help. Most of the time.

— Rex

[Erica R]

In the real mountains one would not choose to set up a tent on wet grass under an open sky.

It is remarkable there was no condensation elsewhere in the tent.

[Roger Caffin]

In the real mountains one would not choose to set up a tent on wet grass under an open sky.
Sometimes one does not have a choice.

(Cabane de Lourdes, France)

Cheers

[john hansford]

 

Nice campsite, Roger. Looks like  you were on the GR10.

Here’s me atop Otchogorrigagna 6307’, a few days walking to the west on the HRP. The wind got up later and I had to drop the Trailstar to a low pitch. Clear skies and grass, but no condensation.

However if you camp in this lot, expect some damp:

.

 

 

 

[Roger Caffin]

Yes, just S of the Barrage d’Ossoue.
Doubt there was any condensation inside.
Cheers

[Mole J]

So where would one set up a tent in “real mountains” ?!

The ones I camp in, the only places to pitch which aren’t uneven rock or bog tend to be on grass under an open sky.  Whether is wet or not is beyond my control!

[Jerry Adams]

if the bottom of the pad has condensation, it must be coming from underneath.  In my opinion.  Water vapor from the air won’t blow under the pad.

even if the floor doesn’t seem to be leaking water, where the pad is, any water vapor will accumulate.  Other places it will evaporate.

and when your weight is on it, that might cause more water to leak through

you could put a piece of polycro under your pad and then the condensation won’t be on the pad, it’ll be on the polycro.  Polycro is waterproof.  An experiment to help figure it out.

 

[Todd T]

if the bottom of the pad has condensation, it must be coming from underneath. In my opinion. Water vapor from the air won’t blow under the pad.

I think you’re underestimating the sneakiness of air. :-)  I’m sure it depends on the kind of pad, how flat it is, how much you move around at night, etc., but I’d expect quite a bit of air to find its way under.  Moisture can no doubt migrate from below too, so…

Polycro is waterproof. An experiment to help figure it out.

[Matt Dirksen]

Water vapor from the air won’t blow under the pad.

Take a dry ziplock bag, put ice water in it, and leave it out on a counter in the home.

Or, put some hot water in the same zip lock bag, leave it outside in the cold on a “bone dry” surface, and see if there’s any trace of “water” on the underside of either of these bags in a matter of minutes. It may take longer in the outside air, especially if it’s real dry and cold, (or it may freeze.)

Water vapor molecules are real small and sticky, and were probably already on the tent floor, well before the pad was put in place. Heck, even the pad probably had vapor molecules all over it, but too small to notice.

No air transport is needed when they were exactly where they needed to be in the first place.

Having this personally happen to me all the time in my climate, (and having witnessed it in failed wall assemblies) there’s no doubt in my mind that I’m swimming in more than enough humidity for condensation to occur, simply due to the thermal difference between two surfaces that are in direct contact with eachother.

The vapor state of water is tricky enough that there are scientists out there that argue it should be considered it’s own phase.

[Tipi Walter]

Greg is onto something.  I have solved the under-pad floor condensation by this technique—Using a ground cloth inside my tent so all the moisture happens between the black floor and the white sheet.  I mark one side of the white sheet with red marker—and this side is always the dry side when packing up and when reaching the next campsite.

In this way I always have a dry surface in my tent.

[Author]

Posts