Abnormal Condensation?

I'd guess that the air in your tent is just reaching the dew point, and so moisture starts to come out of the air. The colder air will be near the floor of the tent (cold air sinks) and this is where the moisture will start to appear. Perhaps the air higher up in the tent is warm enough to avoid the dew point, so no condensation forms on the inside tent walls.

You will only get condensation on the outside of the tent walls if the air outside your tent is moist enough. I suspect in this case it wasn't, and so condensation only occurred inside the tent (where you are adding significantly to the moisture vapor present in the air).

WAG –
John,
What are the objects that collect the condensation?
If it's a waterbottle with 45° F water, I understand.
If it's the front edge of you sleeping bag, I understand.
If it's the cover of your paperback, I'm confused.

Where are they located relative to air flow?
Middle of the tent, or near a vent?

And, perhaps the Tyvek Is accumulating some condensation, but it's soft surface masks its presence?

Given enough clues we can figure this out.
As Ashley said – It's a dewpoint issue in a microclimate.
And maybe by then Roger will be up and online ;-)

Greg

Greg and Ashley, thanks for the help. Both occasions involved a Tyvek tent in dry weather with low humidity. The temps were just above freezing. One occurrence left moisture on the crystal of my watch laying on the floor near the mesh and beads of water the entire length of my sleeping bag and no moisture on the inside of the tent. Waking up and noticing the condensation I ran my fingers over the walls of the tent which were completely void of any perceptible moisture. The second occasion resulted in the upper 1/3 length of my sleeping bag wet and soggy with the tent walls dry as before. Hopefully these somewhat meager added facts will provide sleuthing material allowing you and/or others to explain this to me. With best regards,

John

WAG – Part 2

John-

'The temps were just above freezing.'

'One occurrence left moisture on the crystal of my watch laying on the floor near the mesh and beads of water the entire length of my sleeping bag and no moisture on the inside of the tent.'

Guessing – The watch crystal was below dewpoint temp and a non-porus non-absorbing surface. Tent humidity provided the H20.

Sleeping bag – I am assuming it was that portion of the bag close to the floor of the tent. PU and Silnylon floors are rather waterproof, but not necessarily vapor proof. Water vapor from the ground, warmed by you, moves through the floor hits the colder edge of the bag and presto – condensation. I'd be surprised to see this with polycro ground sheet, with NO pinholes.

'The second occasion resulted in the upper 1/3 length of my sleeping bag wet and soggy with the tent walls dry as before.'

Guessing – typical worst case sleeping bag condensation scenario, where the vapor condenses on the First cold surface it hits and gets trapped there. Anything getting beyond this zone is vented out before coming apparent on the tent wall.

WAG – Part 3

'The only change in my routine is the has been the recent use in the last couple years of a single wall tent with a 360º ring of mesh. … But why would the outside of the tent not experience condensation thus repeating the normal pattern?'

John,
Guessing – IF the mesh perimeter is over bare 'warmish, moist' ground I would guess that vapor is rising from the ground, and moving through the tent. (Vestibule wall are notorious for being wetter than other parts of the tent.) IF this is the case, then when that warm(er) moist(er) air hits something cold, it condenses.

'But why would the outside of the tent not experience condensation thus repeating the normal pattern?'

Guessing – The air Outside of the tent and the tent body are at the same non-condensing conditions. With Tyvek the Inside surface can absorb condensation and move it to the outside.

And interesting test would be to place a 12×12 piece of plastic sheeting on the inside of the tent above your head wall and observe what happens.

A word of caution here… I can make anything sound plausible ;-)

Greg

Thanks Greg. I don’t recall ever experiencing this in a double walled tent over many years of hiking. Several years ago, however, while using a Z-rest pad I recall droplets of water in the depressions of the Z-rest in cool, wet, and humid weather. I have been using a Pro-lite 3 on both occasions discussed and mention this only on the chance that it might factor in arriving at a plausible answer.

Ahhh, Tyvek! I assumed your question was related to silnylon or spinnaker (non-vapour permeable). With the Tyvek, the heat gradient generated by your body towards the outside will push the vapour through the Tyvek as long as the temps remain above dewpoint. The heat gradient is mostly from your body upwards, so objects lower to the ground will hit dewpoint before the tent wall.

This is much the same phenomenum you get with WPB rain gear. Most of them rely on your body heat to push the moisture through the fabric, so no body heat=no "breathability".

Thanks a bunch to everyone for your assistance in understanding a little bit more the issue of condensation. Allison, thank you for the simple explanation of a technical issue that is above my non-technical brain in such a way I can grasp it, in the broad sense anyway. Appreciate it. With best regards,

John