"This just goes to show, as I mentioned in another post, how
the materials that clothing and bags are made from has only
some to do with how dry things stay.
Gore Dryloft has the same exact moisture transfer as
eVent. It is the same stuff before the eVent is treated
to reduce contamination.
Momentum is basically the same stuff the eVent and Dryloft
are laminated onto.
So your experiences are caused by other factors."
Thanks for the material info and I always know that other factors are in play. That being said, I have used different bivys for nearly 40 years, as bag covers not stand alone shelters, and generally in similar conditions. The old taffeta topped ones never condensed (that I can remember). The OR with Dryloft has a cottony feeling material and in over 40 nights only 3 times have I had condensation, all near freezing (7% of the time). With the Momentum top, in over 20 nights it has had condensation nearly 25% of the time in temps from 20's to 50's, not acceptable to me.
This is almost entirely out in the open and not under a tarp. On a recent, dry, trip in Southern Utah I used the Momentum top and it had condensation 5 out of 6 nights and my partner used my OR with Dryloft and had a little condensation on 1 night. Temps 24-33 degrees. I have not used Event but have been out with friends who have them and they had ice in there bivy near freezing.
I have a Montbell Dry-Tec bag cover on the way to test this winter, hoping it might be more like the OR but lighter. I am beginning to suspect it may have to do with the cottony type material the Dryloft is laminated to. May have to just sew a silnylon bottom onto the Old OR top and bring the weight down to 10-12 oz. and call it good.