A bivy tent, sometimes called a bivy shelter, is a small, one-man “tent” which is a cross between a bivy sack and a small tent (I talk more about bivy sacks here).
It is hard to tell the difference between a bivy tent and a regular one-person tent. Bivy tents normally have tent poles, stakes and a rain-fly is often available. The true bivy tent is shaped like the human body laying on its back: wider and taller at the front end and narrowing as it goes towards the foot area.
This allows for a small amount of movement within the tent, yet still being considerate of not adding too much weight to your overall camping equipment.
Bivy tents come in freestanding and non-freestanding models – the type you select depends on where you plan on camping.
Freestanding models are great if the terrain is hard and winds are light while non-freestanding models are desirable if your camping environment tends to be windy.
They are made of fabric that is both breathable and waterproof, which allows human vapors and moisture escape while repelling rain. Bivy tents are basically single wall tents, so in colder climates, the warm air expelled by humans may collect within the bivy.
Bivy Sacks: the Minimalist Approach
Another tent alternative is a bivy sack. Bivy Sacks is simply a waterproof sack that your sleeping bag goes into. This is a very minimalist approach and is well-suited for those who are out for a short term camping trip who can adapt to minimal comforts. Though very light in weight, they can leave much to be desired.
A bivy sack keeps a camper’s sleeping bag dry and adds about 10 degrees of warmth to just a sleeping bag. Unfortunately, the head is constantly exposed to the elements unless the drawstring is pulled very snuggly.
There are two types of bivy sacks: One is simply some type of coated fabric for waterproofness. These are the cheapest but by far the least desirable. The reason is that they do not breathe and you will end up with a damp sleeping bag from the water vapor your body naturally puts off. A much better type (option two) is one made from a Gortex type fabric. This allows the water vapor to escape during the night, eliminating the problem of dampness.
Some bivy sacks allow for armholes (so you can grab some of your gear) as well as room for a sleeping pad (for slightly more comfort and warmth under your body).