Wet Butt

[jefals]

I've got an Osprey pack with the external hydration sleeve. Tried a couple different 3l bladders; Platypus, with the fill cap at the bottom, and Camelbak with fill cap at the top.
An hour or so into my hike, I can feel my butt getting wet.
After 4 hours of hiking, the bladders seem to have as much water left on them as I would expect - so, there's not a severe leak. But the bottom of the pack - underneath that sleeve is wet.
Could this be condensation? For a while, I has been keeping the bladder in the fridge overnight, so I'd have the cold water while hiking. At that point, I was pretty sure that condensation was the answer. But now I keep the bladder in the trunk of the car overnight, and still have the same problem. What's Goin On???
Thanks!

[Daybreak]

Condensation happens only when the water/bladder temperature is lower than the air temperature. Take some hikes with warm/ambient water. If you're still getting wet, it is not condensation. I've had successful PCT and AT thrus with a platypus and no leak problems as long as I sat the bladder on inside top of the pack. Before using a platypus I would sit on my pack but that over pressured it and pop. Most designs put pressure on the bladder but as you use it, the pressure would be decreased so a minor leak might go unnoticed.

[Traveler]

Have you removed the bladder(s) and felt inside the compartment it sits in to see if the bottom of the compartment is wet? I doubt two or three different bladders would have the same problem, if the bladders do not lose water and the compartment is dry, my guess would be sweat from your back migrating down to absorbent material that holds it.

To determine if any of your bladders are leaking, try slipping inserting the bladder into a large freezer bag. It won't be enough to cover the bladder but will tell you if you have a slow leak in it.

[jefals]

Have you removed the bladder(s) and felt inside the compartment it sits in to see if the bottom of the compartment is wet?

The bottom of the pack, just under the bladder compartment is wet. Before realizing that, I was thinking sweat as an option also. I'm still leaning towards condensation. But I don't know the science - exactly how different in temperature the water in the bladder has to be from the outside air? The bladder's been in the car trunk all night, so not super cool. But it's inside that sleeve -- protected somewhat from the sun -- so possibly a little cooler than outside air. But not a lot.
I don't see anything leaking from the bladder. I can squeeze it hard and nothing leaks anywhere.
A real mystery!

[jefals]

Condensation happens only when the water/bladder temperature is lower than the air temperature. Take some hikes with warm/ambient water. If you're still getting wet, it is not condensation. I've had successful PCT and AT thrus with a platypus and no leak problems as long as I sat the bladder on inside top of the pack. Before using a platypus I would sit on my pack but that over pressured it and pop. Most designs put pressure on the bladder but as you use it, the pressure would be decreased so a minor leak might go unnoticed.

I know one other guy who talks about putting the bladder on top of the pack. Why would it leak if it's inside the sleeve, but not if it's at the top?
Are you saying that small water leaks from bladders under pressure is typical?

[Traveler]

The bottom of the pack, just under the bladder compartment is wet. Before realizing that, I was thinking sweat as an option also. I'm still leaning towards condensation. But I don't know the science - exactly how different in temperature the water in the bladder has to be from the outside air? The bladder's been in the car trunk all night, so not super cool. But it's inside that sleeve -- protected somewhat from the sun -- so possibly a little cooler than outside air. But not a lot.
I don't see anything leaking from the bladder. I can squeeze it hard and nothing leaks anywhere.
A real mystery!

It doesn't sound like you have a leak or condensation, but I would need to know the outside temperatures you are hiking in and the relative temperature of the water being carried to consider condensation, the temperature differential would have to be significant for condensation to be bothersome in most any conditions I can think of. If the probable causes are doubtful, that leave the less probable causes which may include:

Back sweat, especially around the hip belt area that won't breath as well as under the vented back of the back itself. Try using a different pack with the same bladder and see if this continues.

Are you wearing the same pants/shorts/undergarment? If so try changing the combinations and see if there is any change.

Is there any other fluid in the pack that could be leaking?

Does this happen all the time or only on a few occasions? Could you have possibly set the pack down into hidden water like a mossy stump or other source?

Are you hiking with pals that are prone to practical jokes?

[John B]

... Are you hiking with pals that are prone to practical jokes?

That would be wicked funny.

[jefals]

It doesn't sound like you have a leak or condensation, but I would need to know the outside temperatures you are hiking in and the relative temperature of the water being carried to consider condensation, the temperature differential would have to be significant for condensation to be bothersome in most any conditions I can think of. If the probable causes are doubtful, that leave the less probable causes which may include:

Back sweat, especially around the hip belt area that won't breath as well as under the vented back of the back itself. Try using a different pack with the same bladder and see if this continues.

Are you wearing the same pants/shorts/undergarment? If so try changing the combinations and see if there is any change.

Is there any other fluid in the pack that could be leaking?

Does this happen all the time or only on a few occasions? Could you have possibly set the pack down into hidden water like a mossy stump or other source?

Are you hiking with pals that are prone to practical jokes?

I'll just guess that I start out with the bladder maybe 10 degrees cooler than outside. I'm hiking close to 4 hours, with outside temps increasing during the day, temp in that bladder probably not increasing that much.
I'm not camping, so, new underpants each day. Same shirt and pants each day, but they start out dry each day.
No other liquids inside the pack. I do have full, 1l smart bottles in each side pocket, but those bottles are still full at the end of the hike, outside of the bottles and inside the pickets are dry.
I don't take the pack off and sit it down in any wet or mossy areas, and I'm hiking alone...

[Daybreak]

I really suspect it is sweat. My sweat runs down my back in all weather.

Condensation occurs anytime a surface is lower than the air's dew point temperature which is not easy to measure. As moist air migrates to a cold surface, its temp. drops until it's cold enough to condense. Less temp.difference = less condensation. Dry air = less condensation.

My point is how to eliminate condensation as a possibility. Warm water, insulating it , moving it will eliminate condensation issues. Before hiking, try putting the water bladder in the shade for ten minutes. If it's not damp, then condensation is not the problem.

For backpacking, I believe placing a platypus gently on top in a less stressed area without cramming it in a sleeve ensures a longer life . Placing heavy things high and close to your body allows one to stand up straighter. Any issues with balance due to to the higher weight, I offset by using poles. I like cold water, so in warm weather I don't like it next to my back nor on the outside in the sun. On the top I can also wrap it with something to help insulate it. Other hikers have different approaches.

[jefals]

I really suspect it is sweat. My sweat runs down my back in all weather.

Condensation occurs anytime a surface is lower than the air's dew point temperature which is not easy to measure. As moist air migrates to a cold surface, its temp. drops until it's cold enough to condense. Less temp.difference = less condensation. Dry air = less condensation.

My point is how to eliminate condensation as a possibility. Warm water, insulating it , moving it will eliminate condensation issues. Before hiking, try putting the water bladder in the shade for ten minutes. If it's not damp, then condensation is not the problem.

For backpacking, I believe placing a platypus gently on top in a less stressed area without cramming it in a sleeve ensures a longer life . Placing heavy things high and close to your body allows one to stand up straighter. Any issues with balance due to to the higher weight, I offset by using poles. I like cold water, so in warm weather I don't like it next to my back nor on the outside in the sun. On the top I can also wrap it with something to help insulate it. Other hikers have different approaches.

I think I'll next try using the plastic-bag-from-the-store idea. I get your point about putting the bladder in a less stressed area; . However, these hikes I'm doing daily are training hikes - working back up to heavier pack, eventually I'll have a bear can up top. So, I just want to get that bladder to work inside it's sleeve.

[Traveler]

I really suspect it is sweat. My sweat runs down my back in all weather.

Condensation occurs anytime a surface is lower than the air's dew point temperature which is not easy to measure. As moist air migrates to a cold surface, its temp. drops until it's cold enough to condense. Less temp.difference = less condensation. Dry air = less condensation.

My point is how to eliminate condensation as a possibility. Warm water, insulating it , moving it will eliminate condensation issues. Before hiking, try putting the water bladder in the shade for ten minutes. If it's not damp, then condensation is not the problem.

For backpacking, I believe placing a platypus gently on top in a less stressed area without cramming it in a sleeve ensures a longer life . Placing heavy things high and close to your body allows one to stand up straighter. Any issues with balance due to to the higher weight, I offset by using poles. I like cold water, so in warm weather I don't like it next to my back nor on the outside in the sun. On the top I can also wrap it with something to help insulate it. Other hikers have different approaches.

Good points here. Humidity is a large player in condensation along with temperature differential. Ten degrees difference in water temperature in 80 degree weather isn't that much and being in the bladder pouch/compartment would lessen the effect of both temperature and humidity differentials as the colder water will cool the pouch until the water heats up in a short time to ambient temperature. I have never seen condensation at a level that would constantly produce water in volume that would soak through a pack and clothing, but have not been everywhere in all possible weather.

Agreed with Daybreak its a sweat issue unless there is a leak. I think it was stated the lid of the bladder was checked, but I double check mine having cross threaded the lid of a Camelbak once and water squeezed out of it, flooding the pack.

Please do let us know what you find out, its an interesting problem.

[jefals]

Good points here. Humidity is a large player in condensation along with temperature differential. Ten degrees difference in water temperature in 80 degree weather isn't that much and being in the bladder pouch/compartment would lessen the effect of both temperature and humidity differentials as the colder water will cool the pouch until the water heats up in a short time to ambient temperature. I have never seen condensation at a level that would constantly produce water in volume that would soak through a pack and clothing, but have not been everywhere in all possible weather.

Agreed with Daybreak its a sweat issue unless there is a leak. I think it was stated the lid of the bladder was checked, but I double check mine having cross threaded the lid of a Camelbak once and water squeezed out of it, flooding the pack.

Please do let us know what you find out, its an interesting problem.

Humidity isn't a big factor, here in Sacramento. If I ever do figure it out, I'll let you know. I had a similar problem years ago with the Camelbak 3l leaking inside a tightly packed HMG 2400 pack. There was a bear can packed vertically pushing against the bladder. Took that and walked around inside an REI with water dripping from the bottom of the pack. We unpacked it, squeezed that bladder "every way from Sunday" trying to see where it was leaking from. Could NOT get it to leak outside the pack. Couldn't get it to NOT leak inside the pack! Switched to a 2l Osprey. Problem solved. May have to do the sa m e now.

[ldsailor]

I've got an Osprey pack with the external hydration sleeve. Tried a couple different 3l bladders; Platypus, with the fill cap at the bottom, and Camelbak with fill cap at the top.
An hour or so into my hike, I can feel my butt getting wet.
After 4 hours of hiking, the bladders seem to have as much water left on them as I would expect - so, there's not a severe leak. But the bottom of the pack - underneath that sleeve is wet.
Could this be condensation? For a while, I has been keeping the bladder in the fridge overnight, so I'd have the cold water while hiking. At that point, I was pretty sure that condensation was the answer. But now I keep the bladder in the trunk of the car overnight, and still have the same problem. What's Goin On???
Thanks!

I've had this exact thing happen to me with a Zpack. The problem I discovered is, although I could find no leak in the bladder when it was removed from the backpack, it was leaking (probably through the fill cover) due to the pressure against the bladder from all the contents in the backpack. The short term fix was to place the bladder at the top of the internal contents of the backpack, thus relieving the pressure and the leak stopped. This happened last year. This year I played around with packing the contents of my backpack and most significantly, loosened the compression straps. No leaking. I'm guessing you are having the same problem.

[jefals]

good news - it is sweat after all!
Just back from today's hike. Tried the plastic grocery sack advice; put the bladder in the plastic sack and them in the hydration sleeve.
Stopped 4 times while hiking to check. The sack as well as the outside of the bladder stayed dry. Still bone dry at the end of the hike, tho the butt area of my pants are soaking wet!

[jefals]

I've had this exact thing happen to me with a Zpack. The problem I discovered is, although I could find no leak in the bladder when it was removed from the backpack, it was leaking (probably through the fill cover) due to the pressure against the bladder from all the contents in the backpack. The short term fix was to place the bladder at the top of the internal contents of the backpack, thus relieving the pressure and the leak stopped. This happened last year. This year I played around with packing the contents of my backpack and most significantly, loosened the compression straps. No leaking. I'm guessing you are having the same problem.

Yes, I've experienced something similar before. Turns out not to be the case this time.

[Traveler]

good news - it is sweat after all!
Just back from today's hike. Tried the plastic grocery sack advice; put the bladder in the plastic sack and them in the hydration sleeve.
Stopped 4 times while hiking to check. The sack as well as the outside of the bladder stayed dry. Still bone dry at the end of the hike, tho the butt area of my pants are soaking wet!

That is good news indeed, thanks for letting us know the outcome!