I have only been on two trips up until now, and camping with the bivy for 11 days all in all, 5 on the first trip though Scotland and 6 on the other though Scotland, England, France, Holland and Germany.
I have been using tents up until now, and I have to say that there are almost the same moisture buildup in the bivy as a tent would. I had to blow up a dry-bag to keep the moisture away from my sleeping bag. Sometimes if I am not camping under a tree or under another form of cover I have to have a tarp. This was not expected, from the reviews I have read on the web. Although, I have to say that I have not tried other bivy’s yet, so I can only compare my experience with one other tent.
The moisture built up happens even with the bivy opened up a third of the way. If I remember correctly the end near the opening had no condensation while the far end of the bivy did have condensation.
I can give you some numbers to just give a more exact weather and the amount of rain would be about 0.1mm – 3mm, humidity level around 70-99% and pressure level around the 1000mb, I don’t know if this gives you enough information on the weather I’ve encountered in the places I’ve camped, to say in the terms of what I’ve been though is moderate rain with high humidity, but not enough so that the bivy could not dry out during the day time.
Another thing is that I go two holes, one made by one of the poles, you can see from the attached images, and the other on the bivy itself.
I have not forced the pole in or was violent in anyway, and I always used a tarp and did not camp in bushes, so this came to me as a surprise. I have to be honest and say that I did not expect it to be “fragile”. What I mean is, if there are already two hole in the bivy after 11 days of camping, what could I expect from another 20 days or more?
Here is a link to Miles website
Amorn a bicycle 
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