Hi everyone. I have been pondering and testing the use of bivvy bags quite a lot, lately. Now I thought I'd share my ideas with you and hear what you have to say about it. For many years now my standard setup for spring to autumn- use has been: evazote foam mat, synthetic sleeping bag/quilt, tarp (DD Solo). In calm weather conditions I pitched the tarp in a classic lean-to configuration. If there was heavy rain to be expected, I'd simply pitch the tarp lower with angled sides for more shelter. I never had a wet sleeping bag and insects as well as slugs never really bothered me. Avoiding wet meadows or ant heaps helps for that matter ;-). Yet, always having to pitch the tarp against morning dew, even in the finest of conditions, startet to annoy me. So I started looking into bivvy bags: what if I could just drop wherever I wanted and sleep under the stars? And when a rainstorm hits, I'd just zip up the bivvy bag exept for my nose to breathe out and wake snug and toasty the next morning. Using the Snugpak SF Bivvy in clear nights with temps around freezing, it was.... okay. The climate inside the bivvy was rather damp, and so was my sleeping bag in the morning. But not wet, at least. Not until a few nights later, when I tried to sleep through a continuous drizzle. It was dreadful. Everything wet, me trying to lie in a position that would allow me to breathe outside the bag without having rain fall on my face. The next morning, my sleeping bag was not drenched, but its entire surface was wet. I sent the bivvy bag back for not being waterproof. Next I tried the Alpkit Hunka. Climate a bit better than the Snugpak, but nothing substantial. Dampish inside while dry outside. But the nights were fine, my sleeping bag stayed dry. Until again, it rained. Sleeping bag wet. Now I started to realize the physics behind it. Once the membrane is completely coated with rainwater it is sealed and condensation hits you hard. Especially as the cold water cools down the fabric of your bivvy bag. Finally I upped the game by going for a high-end bivvy bag with a eVent membrane which I found for a very good price on sale (Exped eVent/PU). Climate was substantially better than in the Alpkit/Snugpak bags. But it comes at twice the weight (600g). Dry outside - dry inside. However, physics make no exeption for expensive gear, I'm afraid. After a rainy night I woke with a wet/damp sleeping bag. What follows from all this? I am not really sure, hence this post. If I need a tarp to protect the bivvy bag from direct rain, I can - just as I used to do before - leave the bivvy bag at home (and opt for a slightly larger tarp if in doubt). Those other arguments don't convince me, either: - Bug protection - is not an issue for me. - Protection against wind-chill - can be achieved with an ultralight and not waterproof bivvy or by specific tarp setup, crafted wind-barrier, etc. - Higher temp. rating - is far more effectively (in terms of weight) achieved by taking a warmer sleeping bag. As I have narrowed it down now, the only real benefit of using a bivvy bag seems to be being able to sleep under the stars and not minding the dew. What do you think about that?