A bivouac shelter or bivvy (alternately bivy, bivi, bivvi) is any of a variety of improvised camp site, or shelter that is usually of a temporary nature, used especially by soldiers, or people engaged in backpacking, bikepacking, scouting, or mountain climbing.  It may often refer to sleeping in the open with a bivouac sack, but it may also refer to a shelter constructed of natural materials like a structure of branches to form a frame, which is then covered with leaves, ferns, and similar material for waterproofing and duff (leaf litter) for insulation. Modern bivouacs often involve the use of one- or two-man tents but may also be without tents or full cover.  In modern mountaineering the nature of the bivouac shelter will depend on the level of preparedness, in particular whether existing camping and outdoor gear may be incorporated into the shelter.  .
The word bivouac is French and ultimately derives from an 18th-century Swiss German usage of Beiwacht (bei by, Wacht watch or patrol).  It referred to an additional watch that would be maintained by a military or civilian force to increase vigilance at an encampment.  Following use by the troops of the British Empire the term became also known as bivvy for short. 
Artificial bivouacs can be constructed using a variety of available materials from corrugated iron sheeting or plywood, to groundsheets or a purpose-made basha. Although these have the advantage of being speedy to erect and resource-efficient, they have relatively poor insulation properties.
There are many different ways to put up a bivouac shelter. The most common method is to use one bivouac sheet as the roof of the shelter and a second as the groundsheet. The 'roof' flysheet is suspended along in its ridge line by a cord tied between two trees which are a suitable distance apart. The four corners of the flysheet are then either pegged out or tied down to other trees. Care must be taken to leave a gap between the ground and the sheet to ensure that there is enough air flow to stop condensation.
A basha is a simple tent, made from one or two sheets of waterproof fabric and some strong cord. Generally a basha is made of reinforced nylon with eyelets and loops or tabs located along all four sides of the sheet and sometimes across the two central lines of symmetry. The basha is an extremely versatile shelter that can be erected in many different ways to suit the particular conditions of the location. (The word also sometimes refers to a special type of bivouac sack described below). 
A bivouac sack is a smaller type of bivouac shelter. Generally it is a portable, lightweight, waterproof shelter, and an alternative to larger bivouac shelters. The main benefit of a bivouac sack shelter is speed of setup and ability to use in a tiny space as compared to tent-like shelters. A bivouac sack is therefore a common choice for hikers, cyclists or climbers who have to camp in tight areas, or in unknown areas. A bivouac sack will usually have a thin waterproof fabric shell that is designed to slip over a sleeping bag, providing an additional 5 to 10 °C of insulation and forming an effective barrier against wind chill and rain. 
A drawback of a simple bivouac sack is the humidity that condenses on the inner side, leaving the occupant or the sleeping bag moist. Moisture severely decreases the insulating effect of sleeping bags.  This problem has been alleviated somewhat in recent years with the advent of more waterproof, but breathable fabrics, such as Gore-Tex, which allow some humidity to pass through the fabric while blocking most external water. A traditional bivouac bag typically cinches all the way down to the user's face, leaving only a small hole to breathe or look through. Other bivouac sack have a mesh screen at the face area to allow for outside visibility and airflow, while still protecting from insects. Fully zipping up a bivouac sack is poor practice, both from the obvious risk of hypoxia, and the dramatically increased levels of condensation that will form inside the bag.
In the German region of Saxon Switzerland in the Elbe Sandstone Mountains climbers refer to overnighting in the open air as Boofen (pronounced "bo-fen").  The spot selected for overnight stays usually comprises an overhang in the sandstone rock or a cave, the so-called Boofe ("bo-fe"). This has often been adapted with a sleeping area and fireplace. In the national park itself, Boofen is only permitted at designated sites and only in connection with climbing, although in this case lighting fires is absolutely forbidden. The colloquial Saxon word boofen was derived from pofen (= sleep soundly and for a long time).
Count Henry Russell-Killough, the “hermit of the Pyrenees”, is broadly accredited with the invention of the bivouac in extreme, inhospitable places. He would bivouac in the open, creating a blanket of rocks and earth or using a simple bag. 
An example of a bivouac being made in a time of urgency was shown when the climber Hermann Buhl made his ascent of Nanga Parbat in 1953 and was forced to bivouac alone on a rock ledge at 8000 m altitude, in order to survive until the following morning. 
Modern bivouacs have evolved to offer heightened levels of comfort for climbers and explorers. Modern portaledges (the vertical camping version of a tent) are a more comfortable, safer, and sturdier option to hanging hammocks. 
Mountaineering, mountain climbing, or alpinism, is a set of outdoor activities that involves ascending tall mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas. Indoor climbing, sport climbing, and bouldering are also considered variants of mountaineering by some.
A backpack—also called knapsack, schoolbag,rucksack, rucksac, pack, sackpack, booksack, bookbag or backsack—is, in its simplest frameless form, a fabric sack carried on one's back and secured with two straps that go over the shoulders, but it can have an external frame, internal frame, and there are bodypacks.
Camping is a form of outdoor recreation involving overnight stays with a basic temporary shelter such as a tent. Camping can also include a recreational vehicle, a permanent tent, a shelter such as a bivy or tarp, or no shelter at all. Typically, participants leave developed areas to spend time outdoors, in pursuit of activities providing them enjoyment or an educational experience. Spending the night away from home distinguishes camping from day-tripping, picnicking, and other outdoor activities.
A tent is a shelter consisting of sheets of fabric or other material draped over, attached to a frame of poles or a supporting rope. While smaller tents may be free-standing or attached to the ground, large tents are usually anchored using guy ropes tied to stakes or tent pegs. First used as portable homes by nomads, tents are now more often used for recreational camping and as temporary shelters.
A sleeping bag is an insulated covering for a person, essentially a lightweight quilt that can be closed with a zipper or similar means to form a tube, which functions as lightweight, portable bedding in situations where a person is sleeping outdoors. It is also commonly used indoors for people who do not have beds or at sleepovers for when one or more persons cannot all fit in the bed or do not feel comfortable sleeping with someone. Its primary purpose is to provide warmth and thermal insulation through its synthetic or down insulation. It also typically has a water-resistant or water-repellent cover that protects, to some extent, against wind chill and light precipitation, but a tent is usually used in addition to a sleeping bag, as it performs those functions better. The bottom surface also provides some cushioning, but a sleeping pad or camp cot is usually used in addition for that purpose. The bottom surface of a sleeping bag may be moderately water repellent, but a plastic tarp or groundsheet is often used to protect against moist ground.
In Australia, a swag is a portable sleeping unit. It is normally a bundle of belongings rolled in a traditional fashion to be carried by a foot traveller in the bush. Before motor transport was common, foot travel over long distances was essential to agriculture in the Australian bush. It is sometimes referred to as a "backpack bed". Swags have been carried by shearers, miners, the unemployed, and many others, some of whom would have been happy to have been called swagmen and some not.
Bivouac is a type of camp or shelter. The term may refer to:
Backpacking is the outdoor recreation of carrying gear on one's back, while hiking for more than a day. It is often an extended journey, and may involve camping outdoors. In North America tenting is common, where simple shelters and mountain huts, widely found in Europe, are rare. In New Zealand, hiking is called tramping and tents are used alongside a nationwide network of huts. Hill walking is an equivalent in Britain, though backpackers make use of a variety of accommodation, in addition to camping. Backpackers use simple huts in South Africa. Trekking and bushwalking are other words used to describe such multi-day trips.
A basha is a waterproof canvas or plastic sheet with eyelets or loops on the perimeter, which is used in camping, outdoor, or military situations to act as a shelter, in the form of an impromptu tent and/or groundsheet, usually supported with rope or even bungee cords attached to trees.
Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or underwater to specified depths.
A fly refers to the outer layer of a tent or to a piece of material which is strung up using rope as a minimalist, stand-alone shelter. In basic terms, a fly is a tent without walls. Purpose-made stand-alone flies are also sometimes referred to as bivouacs, bivvies, tarpaulins, or hootchies. Flies are generally used for keeping moisture or sun off people while they eat, rest or sleep. They can also be used as groundsheets, but this is not recommended since it creates wear and tear which can lead to holes.
A portaledge is a deployable hanging tent system designed for rock climbers who spend multiple days and nights on a big wall climb. An assembled portaledge is a fabric-covered platform surrounded by a metal frame that hangs from a single point and has adjustable suspension straps. A separate cover, called a stormfly, covers the entire system in the event of bad weather.
Fjällräven is a Swedish brand specialising in outdoor equipment—mostly upscale clothing and luggage. It was founded in 1960 by Åke Nordin (1936–2013). The company went public in 1983 with an over-the-counter listing in Stockholm. Since 2014, Fjällräven has been a subsidiary of Fenix Outdoor International AG, which is listed on the Stockholm Stock Exchange. The group also includes the Tierra, Primus, Hanwag, Brunton, and Royal Robbins brands. The CEO of Fenix as of March 2018 was Martin Nordin, the oldest son of Åke Nordin.
Ultralight backpacking is a subset of lightweight backpacking, a style of backpacking which emphasizes carrying the lightest and least amount of gear. While no technical standards exist, some United States hikers consider "ultralight" to mean an initial base weight of less than 4.5kg. Base weight is the weight of a fully loaded backpack at the start of a trip, plus the gear inside and outside it, excluding consumables such as food, water, and fuel. Base weight can be lowered by reducing the weight of individual items of gear, or by choosing not to carry that gear. Ultralight backpacking is most popular among thru-hikers—those hikers on extended trips requiring resupply.
Hammock camping is a form of camping in which a camper sleeps in a suspended hammock rather than a conventional tent on the ground. Due to the absence of poles and the reduced amount of material used, hammocks can be lighter than a tent, though this is not always the case. Most hammocks will also require less space in a pack than a similar occupancy tent. In foul weather, a tarp is suspended above the hammock to keep the rain off of the camper. Mosquito netting, sometimes integrated into the camping hammock itself, is also used as climatic conditions warrant. Camping hammocks are used by campers who are looking for lighter weight, protection from ground-dwelling insects, or other ground complications such as sloped ground, rocky terrain and flooded terrain.
Hiking equipment is the equipment taken on outdoor walking trips. Hiking is usually divided into day-hikes and multiple-day hikes, called backpacking, trekking, and walking tours.
A tarp tent is a tarpaulin, a plastic or nylon sheet, used in place of a tent. It is usually rigged with poles, tent pegs, and guy lines. Ultralight backpackers use tarp tents because they are lightweight compared to other backpacking shelters.
Mountain Hardwear is a subsidiary of Columbia Sportswear based in Richmond, California that manufactures and distributes apparel, accessories and equipment primarily for the high performance needs of mountaineering enthusiasts and outdoor athletes, as well as for consumers who are inspired by the outdoor lifestyle.
Big wall climbing is a type of rock climbing where a climber ascends a long multi-pitch route, normally requiring more than a single day to complete the climb. Big wall routes require the climbing team to live on the route often using portaledges and hauling equipment. It is practiced on tall or more vertical faces with few ledges and small cracks.
Sleeping bag liners are lightweight cloth sacks usually fitted inside sleeping bags to provide extra comfort, insulation, and help keep the sleeping bag clean.