The bivvy sack is as simple as outdoor shelters get. If you can handle being in a confined space it’s a good substitute for a heavy dome tent. You can lie in the warmth of your sleeping bag and watch the stars or get a full view of sunrise in the morning without have to get out of the bivvy. With a bivvy, you can arrive at camp, crawl in, and go to sleep.

Weatherproof Bivvy Sack

A stormproof bivvy is one that is that can prevent water from entering from the outside. It is suitable for use in bad weather as a standalone shelter. Water can get inside a bivvy either through the fabrics, the seams or the opening of the sack.

Gore-Tex is commonly used as a waterproof/breathable fabric in stormproof bivvies. To prevent condensation, fabrics in stormproof bivvies need to allow vapor from perspiration to escape to prevent condensation.

The floor of these waterproof bivvies are made of waterproof fabrics as well but not necessarily breathable. Silicone-coated nylon is typically used for the floor. It functions to keep out water from seeping in through the floor fabric from the ground. It’s important for the floor to able to maintain its waterproof properties so it has to be durable as well.

A stormproof bivvy would also have sealed seams and waterproof closures to be sure that no water can leak in.

Water Resistant Bivvy

If a bivvy sack does not have a waterproof fabric, sealed seams or stormproof closure it is only considered as water-resistant. Sometimes water-resistant bivvies are better than stormproof bivvies.

The obvious advantage for a water-resistant bivvy is that they’re much because of the lack of waterproof features like the seam sealings and waterproof closure. Waterproof fabrics add a little bit of weight as well.

Another advantage of water-resistant bivvies is that they tend to be less prone to condensation because the fabric used is much more breathable. The type of fabric used removes vapors very quickly before it has the chance to condensate.

Combined with a tarp, this type of bivvy works very well. This may mean you have to carry some extra weight but only a small amount of tarp is required and you may not have to worry about condensation so much.

Advanced fabric technology still cannot eliminate the risk of condensation inside a bivvy sack but one day it probably will. Condensation occurs when a warm body in a confined space is mixed with cold temperatures outside. Places inside the bivvy sack where there is a lack of ventilation or body heat is where condensation is likely to occur. The risk is increased when the weather is humid but if there is good ventilation it is less likely to occur.

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