Snow is an excellent heat insulating material, comparable to leather and asbestos. The heat of the body quickly warms a small snow structure to the freez­ing point of water (32° F), provided the snow walls are thick enough (at least one foot), and that all ventilation which is not necessary is excluded.

The amount of fresh air needed for a human being at rest is usually overestimated. Under resting conditions only 0.01 cubic foot of oxygen is consumed each minute. One cubic foot of air per minute for each man is then more than ample. This amount will permeate the un­packed snow around a bivouac. There is then no danger of suffocation from being completely "snowed in" so long as the cave is not glazed with ice.

A small stove consumes more oxygen than twenty men at rest. It may also produce poisonous carbon monoxide. Common prudence requires adequate ventilation while a stove is in operation.

If snow is too loose to cut into blocks for construct­ing bivouacs and igloos, it can frequently be consoli­dated by thoroughly tramping an area, first with skis, then with boots. But this is hard work.

Fir and pine boughs are an excellent substitute for air mattresses and even sleeping bags in emergencies. They can be used, not only on the snow floor, but also as a lining on the sides and roof. The thicker and denser the mat of boughs, the better the insulation and springiness. If evergreen boughs are not available, twigs from decid­uous trees, dry moss from trees or tundra, dry grass and brush may be substituted.

A good place for the boots is in a hole under the sleep-ing bag. The hole should be lined with boughs, extra clothing or other insulating material, except on top. If this is done carefully, the boots will not freeze during the night. Equally effective, but more uncomfortable is to take your boots to bed with you—but take them off. Boots can also be thawed over the cook stove—but don't get the leather hot.

Warm air rises. The best way to keep it in a tent, cave, or other shelter, is to take care that the upper portion of the shelter does not provide excessive opportunity for warm air to escape. Where practicable with caves or igloos, construct the entrance below the level of the main floor area; that is, tunnel up to the floor. Where a low entrance is impracticable, improvise a door of brush, cloth, or snow blocks sealed at the top, leaving the air opening near the bottom.

However, during cooking operations adequate ventila­tion should be provided especially in impermeable tents for the reasons previously stated. Also, reasonably con­trolled ventilation from the top of a tent prevents exces­sive condensation of moisture and is desirable not only during cooking, but also while resting and sleeping if the need for conserving warmth is not imperative.

Overinflated air mattresses are hard and uncomfort­able. Skiers with big hips should dig a hip hole whether or not it is overlain by fir boughs or an air mattress.

Wet socks and innersoles can be dried on a good day by tying them outside the rucksack. On bad days they may be dried against the belly, a method which can also be used at night if necessary; however, it increases the moisture which will be condensed in the bag or tent. Be­cause of the low rate of blood circulation when one is lying down, socks should not be dried on the feet.

Sleeping too warm is undesirable. Even though one is not conscious of perspiring, water is always being evapo­rated from the skin surface. In extremely cold weather this moisture will condense as frost in the outer layer of the sleeping bag, impairing its insulating value and neces­sitating frequent drying.

Drying the sleeping bag by hanging it on a branch or rock during the noontime stop, whenever the sun is shining, is the best method of insuring a warm sleeping bag at night. This should be routine, since even moisture that cannot be felt will decrease the warmth of the bag.

An excellent method of having water ready for a hur­ried breakfast is to dig a hole in the snow, line it with grub bags and just before turning in at night place a full pot of boiling water in this lined hole. Cover pot with more bags and snow for insulation. In extremely cold weather at least a foot of snow cover is needed.

Never leave articles scattered around the snow. They should be either in the tent or in the rucksack. An extra waterproof bag or two is excellent for miscellaneous small articles.

To expedite the work of making camp, members of the party should be given certain duties, such as cooking, collection of firewood, or preparation of tent sites. Time and effort spent in preparing for a good rest and sleep is time well spent. Camp is the best place for the repair of both personal and community equipment. It is also the best place for recuperation of any member of the party who has shown signs of weakening. Timely attendance to his rest and warmth may save the party trouble later.

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