Best warm/humid weather bivy?

I guess my question would be why do you want to be in a bivy on a warm, humid night? Is it for mosquito protection? It seems many UL'ers around here opt for either mosquito netting or a bivy, but not both, depending on the expected conditions.

If you are like me, however, and like to come fully prepared, or change elevation a lot so you may encounter BOTH humid nights AND cold nights in the same trip, the only advice I can give is to bring BOTH a bivy and mosquito netting. The lightest fully-enclosed solution I have been able to come up with is to take a SMD Serenity NetTent or a MLD Serenity Shelter and sew a bivy top onto the silnylon floor, creating a hybrid bivy-net tent combo. Or you could buy a bivy and sew netting around the edges and seam-seal the perimeter (where you made all the holes adding the netting). On warm, humid nights you simply sleep on top of your bivy, inside the mosquito netting. When it cools off, you can slip into the bivy. In the morning, when it warms up again, you are still protected from bugs.

Comfortable in a bivy on a hot/humid night (that's not netting on top)? Not likely. But aside from begging the question…

Bivy's with Momentum or Pertex Quantum tops would be your best bet. Both have DWR's that are fairly effective at repelling water. Momentum is reported a little more water repellent than PQ.

If you don't need water resistant, then just plain uncoated nylon in the lightest weight you can get would breath best. Bivies with eVENT tops are waterproof and quite breathable, but not as breathable as the water resistant ones.

Do you need anything at all?

When I tarp/bivy camp, I will simply sleep inside an equinox bivy (water resistant, ~$60) with no sleeping bag. It works for me.

I am leaning toward bivys because I want to minimize setup/takedown time, and I like being able to sleep under the stars. I really wanted something with a design like the Outdoor Research Advanced with its flip-up/down top, so that I could sleep with my head out minus mosquitos, then simply reach up to flip the top down if it starts raining without having to get up. But it looks like this design is only available in Goretex, which will be too hot and moisture trapping for the summer here in humid Wisconsin/Illinois.

A bug bivy with a tarp over the top sounds like a good hot weather alternative, but if I get hit by rain and strong winds, won't I get soaked? Maybe I'm not understanding the best way to set up a tarp for this. Anyone have a link to a picture, or a description?

The wet-in-the-rain concern was why I was thinking of a water resistant top material, but thinking more about it, even being under nylon sounds uncomfortable for those hot humid nights.

Sounds like you are looking for a wp/b bivy. I would recommend going with eVENT, but having a shelter option for when it's too hot and humid for the bivy. For example, you could combine a bivy with the SMD Wild Oasis. This is a shaped tarp, which should minimize spray from the sides, and it has full bug netting. This way you can just use the bivy on clear nights, or stake out the tarp for a protected zone from mosquitos and sleep on top of your bivy. For the coldest, windy nights use both. If you can afford a 2-layer eVENT bivy from Ron at mountainlaureldesigns.com, this will keep the total weight down to 23oz., which is sill lighter than any of the eVENT bivys I am about to describe. Or, get a Montbell Breeze Dry-Tec bivy at a fraction of the cost and even lighter, but it's slightly less breathable and does not have mosquito netting option like Ron offers.

The closest stand-alone 3-layer eVENT bivy to the OR Adventure bivy is the Integral Designs eVENT Crysallis. It's got waist-length mesh and a flip top, but will be much more breathable and lighter. Unfortunately the flip-top design is not the best for humid conditions; you would feel like you are suffocating if you had to close it all the way, and you'd be pumping a great deal of moisture into your bivy from your breath–not a good idea in already humid conditions.

Unfortunately there are no eVENT bivys on the market that have waist length mesh and allow you to directly breathe out of the bivy when zipped up (by directly breathing I am referring to designs such as the ID South Col and Micro Bivy, with the opening facing your feet. It was amazing to me the difference in comfort I felt when trying out a Micro Bivy vs. a Crysallis; with the Micro I was able to cinch everything down nice ant tight and still be able to see outside and breathe fresh air. With the Crysallis, I was claustrophobic and only got traces of fresh air through the small breathing hole).

I wouldn't do a bivy in warm / humid weather except a mesh one for bug protection (like the A16) with a tarp when I need protection from rain.

If it's warm I was air circulation which a bivy blocks. Given your design for fast setup / takedown I would recommend one of the fast pitching tarptents since as the tarptent contrail, gossamer gear the one, etc. They can be set up in 2 minutes.

well, since it will probably take as much time to set up my little k-mart 2 man tent as it will take to set up and stake down a tarp, and since size/weight isn't a big deal to me since I do most of my camping from a canoe (no places to hike with campsites around here), I will just stick with my little k-mart 2 man tent.

Thanks a lot for all the info guys, you saved me from spending an arm and a leg on something that wouldn't do what i hoped it would do!

A new bivvy from Rab looks as if it might be what you're looking for. The Rab Ultra Bivi is made from Pertex Endurance and weighs 225g. The website describes it as the worlds first welded stitch free bivi.
http://www.rab.uk.com/products_shelter_ultra.html

I do the same as John and if there are bugs out I just use my momentum bivy without a sleeping bag. If it starts getting above 90 though a second bug bivy would be appreciated just don't want to carry it.