Bivvy bag - Emergency sleeping bag

Are you and your car ready for the next winter storm? A bivvy bag can be the difference between an uncomfortable night and a dangerous one.

The interstate that shuts down and leaves you parked in the snow. The ice storm that knocks out power for two days. The hike that runs long. When it happens, warmth is the first thing you lose – and the hardest thing to get back. The bivvy bag is built for exactly these situations: climb in, pull it closed, and let your own body heat stay with you instead of disappearing into the cold.

The difference from a regular sleeping bag is that this one is always with you. It takes up so little room that you can keep one in every vehicle, one in the emergency kit at home, and one in your pack – and never notice it until you need it.

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Be ready for the unexpected

Four reasons to put one in your kit today

Losing heat with and without an emergency sleeping bag

Picture being stuck in a cold car for a full day and night before help reaches you. Here's how the two situations differ.

But doesn't it get damp inside?

It's the question we get most often, and the answer is that some condensation can occur. But how much depends on how warm your body is. A chilled body in the cold gives off far less moisture than a warm body that's working. This bag gets used at rest, in the cold – and in those conditions, moisture is rarely what decides the outcome.

Think of a down jacket worn over nothing but a t-shirt. If you're hot and sweaty, the lining sticks to your skin immediately. If it's 20°F out, you can wear that exact same jacket without it sticking anywhere. The emergency sleeping bag behaves the same way: the colder it is, the less you notice the moisture.

And the real question isn't whether it might get a little damp. It's: a down jacket that might stick, or no jacket at all?

Medical guidelines for hypothermic patients specifically recommend a vapor barrier of plastic or reflective foil used together with insulation. The vapor barrier reduces cooling from air movement and evaporation, and keeps the outer insulation dry. Studies show the effect holds even when the person is already in wet clothing.

How to get the most out of your bivvy bag

Preventing hypothermia

The emergency sleeping bag does the most good as part of a system. The principle is called the hypothermia wrap, and it's built from four layers: insulation under the body, dry clothing or blankets closest to the skin, the emergency sleeping bag as a vapor barrier, and extra warmth on the outside.

From the bottom up:

• Insulate against the ground or the car floor – that's where most heat is lost.
• Change or wring out soaking wet clothing if you can, before the person climbs in.
• The emergency sleeping bag closest, as a wind, water, and vapor barrier.
• Blankets, sleeping bags, or jackets outside the bag – never inside it.
• Keep the head and airway outside the bag.

To cut condensation further: keep activity low inside the bag, take off a layer before climbing in if you're sweaty, and vent briefly if moisture starts to build up.

Sources: Wilderness Medical Society practice guidelines for hypothermia and a randomized field study on vapor barriers (PMC10809790).

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Specs: Bivvy bag emergency sleeping bag

Note: The Bivvy bag is an emergency sleeping bag built for emergencies. If you're car camping or planning to sleep outdoors, we recommend our regular sleeping bag – compact and light, but built for several nights in a row.