quilts bivvies and condensation, one confused Englishaman’s cry for help…

[Joseph Williams]

Dear all, as a new bod from england who is very keen to try out this lightweight, home sewn business, I've been fascinated to trawl everyone's input to this forum. It's delighted me to see so much creative energy and advice being shared so freely.
I'm trying to design a lightweight sleep system for myself, based on a poncho tarp and a synthetic quilt, and I was hoping that someone could give me some pointers about how best to manage condensation.

I was impressed by David Willis' quilt project with it's unbroken layer of water resistant momentum fabric on top- http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/4439/index.html – , and thought this sort of design, combined with a generously sized tarp would allow me to dispense with a bivvy sack. But I am worried that this approach will simply move the location where the air reaches dew point to inside the quilt, between the top fabric and the insulation. Only experience will tell me if this is the case, and having none of my own, I'm hoping to borrow someone else's. Any thoughts?

If a bivvy is needed, ( I would make the lightweight, semi-waterproof type, probably from momentum and sylnylon) should I still shell my quilt with a DWR fabric, or would this be just too much DWR between me and the outside air, creating excessive condensation?
My standard DWR shelled sleeping bag and heavyweight Gore-tex bivvy setup works by wicking moisture up to between the sleeper and the bivvy, and sleeper's DWR shell stops any excess sinking back down into the insulation. This would suggest the need for both a sack and a DWR shelled quilt. Or could I get away with a non-dwr upper on the quilt, leaving me totally breathable on fine nights where the bivvy stays rolled up in the sack?

I will use this setup in the UK, so low altitude, mild climate, but with westerly winds and a fair amount of rain.

I know this is a lot of questions, to which there will not be any definitive solution, but I would be interested to hear anyone's opinions, and would be grateful for any advice offered. Part of the obsession with detail is that we just don't have the supply of materials in this country, so I'm going to have to calculate my fabric requirements really carefully, and hopefully only pay one lot of postage from AYCE at thruhiker!

All the best,
Joe

[Aaron Sorensen]

Hey Joe,
I am going this same route but with the added bottom to make it bivy-like, (hold more heat in).

I will also be making one using Thru-hiker 1.8 ounce prequilt that I will attach baffles to to put down on the bottom while still having an unbroken layer on top.

To put the bottom on making it more bivy-like I will just have a few pull cords to sench it around me. It will also contain the 1/8" pad that will curve around the sides of my body to hold in the warmth, (I am not a side sleeper so it will work for me).
The quilt part will also tuck underneath the bottom.

If you are going to go this route, especially with the Momentum fabric, I would not use a bivy.
Isn't that what we're tiring to eliminate anyway?

This would also compliment smaller tarps/capes because you don't have to worry about getting a little drip here and there.

GO FOR IT!

It will work better than you may be doughting it will.

[Joseph Williams]

hey Aaron sounds like there's a lot of confidence in the wind/water repellancy of Momentum fabric. Sounds' like it'll be fine at reppelling water from the outside. All I'm thinking is that there's going to be a layer of fabric with a big temperature across it (causing condensation) at some point in the system, so shouldn't that be between the quilt and a bivvy, rather than the outer layer of the quilt itself, which will be laying directly on the insulation. What do you think?

[Aaron Sorensen]

Hey Joe,
I'll let some one else answer that.
If it's the lighter way to go, I'm going that way, (that's my reply any way).

[Joseph Williams]

good stuff. I reckon the best thing for me to do is make both systems and let the great water laden westerly airstream decide!

all the best,
J.

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