Campers have many options for shelter. Devoted minimalists might take nothing beyond their sleeping bag, or simply rig up a tarp to keep the rain off of their heads. For most campers, though, tents are the standard, although backpackers who don’t want to haul much weight sometimes prefer the bare-bones shells called bivy sacks.
Identification
Bivy (bivouac) sacks are basically exterior shells for your sleeping bag, contoured in roughly the same shape with the maximum volume around the head area. Tents come in a great array of shapes and sizes, with some of the most compact and specialized resembling a more spacious, rigid bivy sack; these are sometimes called “bivy tents,” and are often used by ultra-light backpackers and mountaineers. Much larger and bulkier tents suitable for family car-camping can accommodate many sleepers.
Weight and Space
Bivy sacks often weigh less than tents, which is perhaps their chief advantage. Ultra-light backpackers--those who aim to tote fewer and lighter supplies into the wilds--often choose bivy sacks, which can weigh as little as 2 lbs. They also tend to take up less room in a backpack than a tent.
Set-Up
Bivy sacks usually slip around the outside of a sleeping bag, essentially functioning as an exterior cover. Certain models incorporate poles to increase space around the sleeper’s head. Tents vary widely in set-up: Some A-frame models employ ropes and stakes in the manner of a minimalist tarp shelter, while many standard dome tents use a number of poles and stakes in a self-supporting configuration. Especially under dark or inclement conditions, the more complicated tents will be more difficult to erect than bivy sacks.
Protection
Tents offer greater protection and shelter from the elements than bivy sacks. A sturdily framed tent, whether a dome model or an A-frame or bivy tent, is more stable in the face of heavy gusts. Many tents incorporate a separate rainfly that guards against precipitation and also wicks condensation from the body of the shelter. Single-wall tents, which include many mountaineering bivy-style models, don’t use a rainfly, since their Gore-Tex or other specialized material is waterproof and breathable. Many bivy sacks feature the same single-wall construction, but some have only mesh around the head, an obvious drawback in rain. The sacks do, however, confer notable insulation to your sleeping bag: In "The Backpacker’s Field Manual," Rick Curtis suggests that they might bolster your bag’s temperature rating by 10 or 15 degrees F. For this reason, some backpackers use bivy sacks in conjunction with a tent.
Space
The interior of most tents is naturally more roomy than that of bivy sacks, which provide only enough space for sleeping: Even changing clothes usually needs to be conducted outside the bivy sack. There usually is enough room, however, for dealing with flashlights, removing contact lenses and other essential nighttime routines. As Len McDougall notes in "The Outdoors Almanac," for those who border on claustrophobia, the bivy sack is likely a less-than-desirable shelter. Tents give the occupant the option of sitting up, changing and relaxing--important considerations, especially if you might be holed up by bad weather for a spell. Unsurprisingly, larger models of tents are the preferred option for multiple sleepers.
References
- "The Outdoors Almanac"; Len McDougall; 1999 (pgs. 36-37)
- REI: How to Choose a Backpacking Tent
- "The Backpacker's Field Manual"; Rick Curtis; 2005 (p. 48)
- "Joy of Backpacking"; Brian Beffort; 2007 (p. 79)
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