For the uninitiated, a kisu/bothy bag is basically a simple pu waterproofed nylon tent, open at the bottom, with a draw cord round the base. In use, the people inside become the tent poles, pulling in the draw cord and sitting on the skirt which is formed inside. They have been around a long time, the larger versions gaining popularity with rescue teams and instructors, but the average mountaineer will probably go for the 1-3 man size.

As a piece of winter emergency kit, they have several advantages over a bivi-bag. The most immediately noticeable is that 2 or more peoples' body heat makes for a surprisingly warm environment in which to regroup, sit out the night, or just eat your butties. I have used these on Arctic ski treks and found that two of us could comfortably eat lunch, gloves off, with a minus 10 blizzard blowing outside. Other plus points are that you can keep your crampons on, the sitting position is practical and good for morale and one bothy bag is lighter than two bivi-bags.

The JDS Components versions of the kisu/bothy bag meet the main criteria of simplicity and robustness and have the kind of cheery yellow colour that fools you into thinking the weather has cleared up outside. They incorporate all of the basic features you need; a couple of Velcro-sealable vents, integral stuff sac and draw cord. They also have loop tabs at the corners, which opens up more options below the tree line.

JDS bags are currently in use with a number of mountain rescue teams and mountain guides. They come in three sizes and are available direct from the manufacturer.