A bivy sack is a portable device used in conjunction with or in place of a tent when ultra-light backpacking or hiking. It can be use as an emergency shelter for short hikes, as well.
Step 1:
Purchase the following:
6’x 8′ blue/silver poly tarp. ($4.88 at the writing of this article)
Small roll of duct tape ($1)
Box of 12 1 ¼ inch clamp style paper clips ($1.37)
Step 2:
On a large flat surface such as a garage or living room floor, spread out your tarp, silver side up.
Step 3:
Fold the tarp in half lengthwise, making a 3′ wide x 8′ long rectangle with the blue side out.
Step 4:
Duct tape the foot end, sealing the edges together.
Step 5:
Turn the “soon to be bag” inside (silver side) out and retape the bottom from the inside.
Step 6:
With the bag still inside out, fold the loose edges on the side so they overlap about 2 inches (imagine making a tube where the edges overlap and only one edge is taped). Start at the bottom and begin taping your way up the length of the loose side. Tape the entire first two feet from the bottom (foot), then skip 6 inches, tape 6 inches, alternating to about 4 or 5 feet from the foot.
Step 7:
Turn the bag back right (blue) side out.
What you have now is a bivvy that is 3′ wide and 8′ long. The poly tarp is cheap, easy to replace and fairly durable.
There is a definite top and bottom. The overhanging edge along with the areas that are not taped are designed to allow the bag to breathe, while keeping precipitation out by creating an “eave” along the edge that prevents water from coming in. As you move, fresh air with be drawn into the bag and exhaled from it through the gaps in the taped edge, thus negating some condensation.
The clamp style paper clips serve many purposes. They can be used to clamp the top edges to close the bivvy off (remember to position them so water will be shed, not channeled inside!). Leave a space near your face for your breath to escape, of course. A few can be used on the edges of the bivvy then staked or tied down to prevent any tossing and turning from exposing the “eave” to the elements. They can also be used in conjunction with a small stick (stick on the inside with the clamps on the outside) to give you a way to run a small rope to hold the top of the bivvy off of your face/body/sleeping bag.
This bivvy is not hurricane proof, but it’s very functional. It easily compacts into a 5″x10″ roll, too big for a pocket, but plenty small enough for a day pack. In addition, informal tests revealed an 8 degree rise in temperature inside the bivvy versus outside with no mat, blanket, or bag. This was in 55F degree weather. A light rain left me completely dry.
