Group shelter bag and huddling

Outside, the wind immediately carries away the warmth your body gives off into the air. Under the cover the air is still. Every person gives off heat all the time, and in the small, enclosed space it stays put for a while. With several people the air therefore becomes noticeably warmer than outside, and rain and wind are shut out.

Then there is huddling: when people sit close together, shoulders, backs and sides touch. These areas hardly lose any heat to the outside any more. The group as a whole loses less heat than the same people would on their own – a principle also known from animals that huddle together in the cold.

The bag needs neither poles nor stakes, because the people themselves are the frame: heads and shoulders lift the fabric, and sitting on the edge holds it to the ground. That is why setting it up is so quick, even in places where no tent could stand.

The most common mistake is getting the bag out too late. It works best while everyone is still reasonably warm. If you wait until someone cannot go on, you then have to regain warmth the hard way. A break in the rain, a rest in the wind or waiting with an injured person are good moments.

Never sit directly on snow, rock or wet ground. Backpacks, sleeping pads or ropes under your bottom stop the ground drawing away your warmth. The size of the bag should suit the group: if it is too small, someone sits half outside; if it is too big for one person alone, the air inside hardly warms up.

Choose a spot that is as sheltered from the wind as possible, level and safe from rockfall and falls. A brightly coloured bag is easy to see from outside – an advantage when you are waiting for rescue.

The fabric is usually waterproof and windproof, so it also lets in hardly any fresh air. When people breathe they use up oxygen and give off carbon dioxide; in a tight bag the air can therefore become stale over time. Keep a vent or window open and air it briefly at regular intervals. In case of headache, dizziness or shortness of breath, open it immediately.

Stoves, candles or other flames must never be used in the bag: they use up extra oxygen, can produce carbon monoxide, and the thin fabric can catch fire. Warm drinks from a vacuum flask are a safe way to warm someone from the inside.

The group shelter does not replace help. If someone is injured or shows signs of hypothermia – heavy shivering, confusion, listlessness – call the local emergency number (112 in the EU). Until help arrives, the bag is a good place to protect and look after the person.

The group shelter is made for waiting: breaks in bad weather, caring for an injured person, waiting for fog to lift or for rescue. For school groups, guided groups and mountain walks it is a light piece of safety equipment that takes up little room in the backpack.

It is not meant for a whole night. You cannot lie down in it, condensation forms, and without insulation under the body it gets cold over time. Alone it is also not very effective, because one person cannot heat the large volume of air – a single-person bivy bag is better there.

Without a group shelter, huddling still helps: everyone close together, backs to the wind, sheets, emergency blankets or jackets around the outside. This is less effective but much better than waiting separately.

In English the group shelter is often called a "bothy bag". In Britain a "bothy" is a simple, open refuge hut in the hills – so the bag is, in a way, a hut to take with you. It is common among mountain leaders, school groups and mountain rescue.

Practise using it once with your group in good weather. Then everyone knows how to get in, where the vent is and how to tuck the edge under themselves. In a storm there is no time for explanations.