SwampDonkey: Those who don't like tight enclosed spaces need not apply. The is a bit of room but not much. I can get my arms up and out and that's about it.

Many bivy's have something covering your head to protect it from rain and whatnot. Some of these even have what's like a mini tent around your head complete with poles. They are also heavier...they are also more expensive (much more in some cases).

This bivy is not protected from rain where the mesh is (though it does have creative little gutters to keep rain from running up and in at the head). You can either throw something waterproof over your head at night (like a jacket) or sleep under a shelter (anything from a tarp to a tree).


justmeagain: There are a few differences (maybe more). One, the emergency bivy is much smaller/lighter. I think it's just made from more or less standard space blanket materials. The material in the thermo-lite is heavier, has a fuzzy lining (80% radiant heat reflected instead of 90% with the emergency bivy), is sewn all the way around and where it's not there's velcro...and it has a closable mesh foot vent. Plus the Thermolite is designed to be reused...not just for emergencies necessarily (AMK suggests is as standard equipment for ultralighters)