staehpj1

There is no single "one size fits all" answer. It is a balance of weight tolerated vs coverage needed/desired. It also matters whether the bivy is weatherproof or a bug bivy and whether the sleeping bag is DWR coated. Expected weather conditions are a factor as well as are geographic factors like how exposed will you be wrt the wind.

All that said... For most people the little bigger tarp (like the Sea2Summit Escapist M 6'6" x 8'6") may be worth the extra weight and bulk. It allows the tarp to be pitched higher. It allows more room under the tarp. It is a bit more insurance of staying dry and keeping gear dry. At 12 ounces most will find that a good compromise. That doesn't mean some folks can't get by with a small tarp, a tiny tarp, or even no tarp. I did fine with a tiny tarp that only covered the upper half of my bivy on at least one trip and was okay, but it probably was more trouble than it was worth to save 7 or 8 ounces. I could in a pinch cover the opening of my bivy with my wind shirt to shed rain, but that is pretty spartan. I just might go there on a trip where I figured the chance of rain was near zero.

The in between sized Integral Designs Siltarp 1 is a fairly reasonable compromise for the more weight conscious, but not completely weight obsessed.

staehpj1

Yes, it is always a challenge to be comfortable when it is hot and buggy with a regular bivy. I typically use an all mesh topped bug bivy if it will be buggy and hot. The problem is that there is often some of both cold weather and hot and buggy weather on a really long tour. That may be solved by switching bivys at some point in the trip for a long trip. That would have worked for the Southern Tier where I was miserable a couple nights on the Gulf coast if I had planned ahead better and arranged to mail my bivy home and have the bug bivy mailed to me. As it is it was only a couple nights that were miserable. The Louisiana skeeters were really crazy bad and it was kind of sticky hot.

When it isn't buggy, I typically have a range of sleeping arrangements depending on the temperature. I often go through them as it gets colder through the night. I might start out sleeping on top of the sleeping bag and bivy. If it gets chilly I drape the sleeping bag over myself lie a quilt. I get in the bag if it get colder. I zip up as it get colder. I pull the hood drawstring tighter as it gets colder, but always breathe through the opening. If it isn't buggy, windy, or really cold I may not bother to get in the bivy. I often may not bother to pitch the tarp either. If I get unexpected rain when I didn't pitch the tarp I just pull it over myself and my gear. It depends of where I am and what the season is, some trips I may pitch the tarp every night and some not at all.

BTW, just to be clear... In my case I am referring to minimal bivys with no hoops. My Borah Side zipper ultralight bivy is 7 ounces and my Ti Goat Ptarmigan Bug Bivy is 5.3 ounces. The bivys with hoops and what not, often weighing 2 pounds or more are a different animal. Personally if going there I go a step further and go with a tarp tent or even something like my Eureka Spitfire 1 (2 pounds 9 ounces) which I use when I go heavier (which I don't often do these days).

FlippinFlags

Are snakes, spiders, leaches and other bugs a large concern while inside of a bivy?

Happy Feet

I've slept in it from 90+ to -42F. It is gortex and half mesh. I can flip the cover down to my waist. On hot nights I lay on top of my sleeping bag until I get chilly and then slip into it.

shipwreck

The whole point of being enclosed is to keep them out. You might check for the dreaded Copper Headed Rattlebacks outside the exit area in the morning, but no more so than you would in a larger tent.