A cover on top of a down Top quilt, problems?

[novascotia-hanger]

If I put a bivy over a top quilt (or similar over cover, rip stop?) to keep out moisture on the down bag, would the weight of the bivy (zipper on bottom or the side) compress the down and compromise the temp rating? Would it change the loft?

[fallkniven]

That would be a really bad idea. All the moisture coming off you would get trapped in the insulation. Hot or cold, you emit a lot of vapor when you sleep. Unless you used a vapor barrier liner/clothes.
What I do is, I found a really thin, lightweight wool blend blanket at a surplus store for $15. Cut a rectangle out of it just big enough to cover you in the way you described. I only use it in the winter though, keepingg frost off the quilt, and tucking it under my neck so I'm breathing on/over the wool and not the down quilt. The wool will keep you dry from above, but is still highly breathable, and will still retain most of it's warmth . Having a thin blanket cut that small doesn't weigh much, considering what it does for you.

[cjayflo]

If you were of a mind to try a bivy you can find them for cheap from military surplus. Unless you are on the ground I would not recommend it.

[novascotia-hanger]

Thanks for the info, I forgot about moisture form me!!

[Passinthru]

Pertaining to the part of your question about possibly compressing the loft in the down quilt...I think that it could be a concern if a very heavy overquilt was used. I doubt if the weight of a bivy would hurt (already ruled out anyway because of moisture trapping) but maybe a heavier synthetic blanket or quilt over the down would be too much.
As I was considering which temp rating of top quilt to buy I was thinking that I could buy a lighter quilt and just double up with a second quilt in colder temps. I was concerned about the possible loss of loft so I went with a temp rating that will get me to my expected lows without adding a layer.

[IRONFISH45]

I have a Hennessey overcover, it is just nylon, with a round hole cut in it. Lots of air circulation, it was never a tidy fit on the Hennessey, it acts like a bellows each time I move. lots of fresh air in, steamy air out, I really like it because it helps keep me warm, keeps the outside mist off. Not confining like the sock idea. Just a bit extra to help me stay warm and keep the night moisture off. Most of the time I use a tarp also to catch any real mist.

[IAmilz]

I have one of those SOL escape bivvys that I just lay on top of my quilt to keep the dew off.

It's supposed to be breathable so I figure in a pinch I could crawl inside it then get under the quilt for extra warmth if needed.
Haven't tried it yet though.

[nothermark]

I seldom disagree with fallkniven but there is a calibration factor. On a dew free night a cover will trap more moisture than it prevents. OTOH if you are dealing with heavy dew and/or fog the cover will block more than it traps. Basically the wet cover blocks evaporation while adding the load of the dew.

Moisture management is always a balance. The problem is how much moisture a cubic unit of air is holding. If the amount is low then the dew point is very low and one worries about perspiration drying. If the load is high the dewpoint is high and one worries about depositing condensation. Drying take a lot of air moving to pick up moisture while condensation indicates keeping air movement low to limit the amount deposited.

Covers are a good way to manage air movement as needed. The trick is to know what is needed in a given set of conditions. If one has weather information the dew point and predicted low will provide a clue. If now data is available it's an educated guess. One thing that will not be a mistake is to drop a cover over bedding as the temperature starts to drop and make a decision later based on the dew on the cover. It does not take much in terms of weight. I've used my poncho or a space blanket.

[SnrMoment]

I use a top cover suspended from the ridge line that can be pulled over my head or opened to all the way back. End is secured by a velcro closure that goes around the end of the hammock. It can be tucked into the UQP to block wind. Works pretty well around here where the humidity is low. It will pick up moisture from you, but it's off your quilt.

[Peter_pan]

The Dri ducks poncho with the JRB weather shield modification will form a foot box and function as a wind proof/waterproof TQ bivi cover in a hammock, weighs 9 oz and is the most breathable WP material available!...Reasonable poncho, so dual purpose and under $40.... http://www.jacksrbetter.com/shop/dri...n-kit-applied/... Picure shows it in the UQ mode but is a great top bivi as well.

Pan