A bivy sack, otherwise known as a bivouac sack, is a waterproof addition to sleeping bags that goes over the head of your sleeping bag to protect you without having to cover your face with the sleeping bag.
Usually, waterproof bivy sacks are made of the same kind of material that tents are made of.
There are some that just form a tent over the head of the sleeping bag, and some that drawstring all the way down to the user's face with just a small hole to look out of or breathe.
Most of them have two tiers, a top layer with breathable material to allow breathing, and the bottom made of waterproof material.
The ones that form a tent over the head of the sleeping bag are made out of breathable material so that they can allow the heat to stay in and the carbon dioxide to escape.
When you are buying a waterproof bivy sack, there are certain things that you can look for.
First of all, getting one with insulation will keep you warmer.
The idea behind a bivy sack is to keep your face and head protected without having to keep it buried in the sleeping bag.
Since you want your load to be as light as possible, you want one that is light weight and durable for camping and traveling.
Overlapping materials will allow you to not need to unzip it all the way and still be waterproof.
Remember that it is designed also to keep away bugs and moisture off of your face.
Some bivy sacks come with straps to attach to the sleeping bag to get an air tight seal and most now come with factory stitching to make sure that they are durable and water sealed.
While you might think that it is too tight a space for you, it may not be.
The waterproof bivy sack has a sister product called a bivy shelter.
This is a low rise tent with a built in bivy sack at the head.
It is designed for light campers with just enough space to camp.
It offers no space to sit up and while its waterproof, it can be a long wait if you are in an area of persistent rain.
These come with poles and a set up so that the bivy sack does not touch your face or irritate the user.
If you are a long haul backpacker or a light camper, the waterproof bivy bag is ideal.
It is a great way to stay warm without having to bury your head in a sleeping bag and it will work wonders at keeping the rain out of your face, as well as keeping the bugs off of your back.
Whether you just get a bivy sack or a bivy shelter, these products are a great for a night of camping or a lifetime of sleeping outdoors.