A second upper strip is, in over-all dimensions, a duplicate of the first, but for the fact that it is 9 inches shorter. From the foot up and for a length of 78 inches it is identical with the first strip, but at that point it is cut short. A face opening is cut in the upper edge of the second strip, 10 inches across and 11 inches deep.
These two strips are superposed and their overlying edges are sewed together. All edges are properly hemmed or bound.
As the user lies in the bag, his feet just reaching the bottom, his face is encircled in the face opening. The excess length of the under strip then becomes a flap, to fold over his head. Buttons and buttonholes may be provided, as indicated in the drawings, to secure the flap in such position.
The material for the outer layer is cut to the same pattern, with sufficient enlargement of dimensions to allow the outer bag to contain the inner bag and cover it smoothly.
The outer material will preferably be water-proofed balloon silk (“tanalite”); the inner material may be sateen, or blanketing, or down quilt. The designers suggest still another material: Australian wool wadding, encased in sateen. They say, “a brown sateen material is the best covering, as a very finely woven goods is necessary to keep the wool from working through. The bag does not need to be quilted, but should be ‘tied through’ about every six inches.”
The balloon silk outer bag should weigh about one and one-quarter pounds; the bag of sateen should weigh about two and one-quarter pounds. C. F. Hovey Co., 33 Summer St., Boston, and the Abercrombie & Fitch Co., Madison Ave. and Forty-fifth St., New York, have made bags to these specifications.
It remains only to add a word respecting the outer cover of balloon silk. Balloon silk, which in reality is a fine-woven cotton, is, relatively speaking, a delicate material, and furthermore it is not perfectly water-tight. The great advantage of lightness justifies its use. But the bag must be carefully handled, and after hard service the cover must be renewed.
Dr. Charles W. Townsend, of Boston, an experienced camper, writes:
“The sleeping bag is a home-made affair, that takes up only a small part of the room in a rucksack, and weighs four pounds. It is made of lamb’s wool wadding, lined with sateen, and covered with flannel. It is about six and one-half feet long and tapers, so as to be wider at the mouth than at the foot. With ordinary clothing, I have slept warm in it with a temperature of forty degrees. I have also a balloon-silk cover, which can be arranged to guy-ropes, to make a lean-to tent over my head, and gauze curtains for insects. I think that weighs two and one-half pounds.”