I have made a bivi out of a driducks poncho (tan color). It seemed as a good material, the raingear made out of this material is said to be very breathable. It's also cheap, so why not to try.

However, the bivi failed badly in the field. I had quite a lot of condensation on the inside of the bivi every time I used it. I never stayed in it for the whole night, just to the point I realized that I will do better without it. The conditions were quite good for bivi use (no rain, just strong cold wind once, around freezing the other times). A friend of mine using a bivy with gelanots membrane stayed completely dry in the same conditions. I was quite cold on one of the nights, so it is not due to excess sweat. The result was probably the same as sleeping in non-breathable bag (as far as I remember it).

Is there someone with similar experience or someone for whom it works? I'm just curious, my next bivy will be made of something much better. At least I have tested the pattern on a cheap prototype.

Well, that takes care of one idea for a cheap bivy!

That's very strange. I would think it would work great. I know Bill Fornshell has made bivies out of Propore, so maybe the Driducks poncho is made from a different kind of Propore. I know there is a little difference between brands, so maybe that's the problem. It could be because it is sold for a poncho, they used some type of Propore that isn't as breathable. Bill's blog: http://ultraliteskunkworks.blogspot.com/ shows him making it (I think it is the third post down) and I assume it worked out well for him. He has been a huge contributor to this forum, but I'm not sure if he posts here as much anymore. Either way, I would try to get hold of him.

I've used my sleeping bag cover (JRB used to sell them) made out of the same material many times over the years and have never had condensation.

I'm at a loss as to why your had so much...

Check out many previous threads as to why condensation occurs. Often it has little to do
with the materials covering you and more to do with the dew point.