If several persons are bivouacking together the quantity of boughs required for a mattress is reduced and considerable body heat is conserved. Two feet in width should be allowed for each person. A waterproof sheet may be thrown over all the sleeping bags for increased warmth. This will not condense excessive moisture because ventilation is provided between the sleeping bags.
Brush shelter.—If the snow is not deep enough for a snow bivouac a brush shelter can be constructed, in the heart of the densest thicket available and well out of the wind. The design is unimportant provided the walls are interlaced densely for windproofing, and the entire shelter is made no larger than necessary. Covering the brush with bark, snow, or sod will aid windproofing and better retain air warmed by body heat.