It is worth considering somewhat minutely what are the requisites of perfect clothing, and what properties our different kinds of wearing apparel possess. Without doubt any reflection on the question of what is usually worn and what ought to be worn is not only of considerable interest generally, but of great moment likewise from a health point of view. It cannot be maintained too strongly that the question of the proper material for a suitable covering for the body takes a footing nearly equal to the very important one of diet itself. Now, there is no form of clothing which on its own account creates heat, or has the property of bestowing warmth upon the body, but the difference in it consists in its power of preventing the escape of the body heat. These qualities in the different varieties of wearing apparel will depend to a great extent upon the thickness of the materials, and also upon the varying power which they possess in detaining air within their meshes. It is this latter property of retaining the air, which is warmed by contact with the body, in their interstices, which constitutes the great difference in the various clothing materials. This is also an explanation of the well-known fact that loose garments are always warmer than tightly fitting ones, for in the former there is the layer of warm air in contact with the body, which has no opportunity for existing in the latter. In the same way two or three layers of under-garments will always be warmer than a single one, equal to their combined thickness, since there is a separate layer of air between each of the thinner ones.
All the differences in the various fabrics are due in chief part to the properties of heat. The ordinary or normal temperature of the human body is between 98° and 99° Fahrenheit, while that of the air will vary considerably, according to the climate and locality. Each individual, therefore, must be regarded as a material, though living, object which is enveloped in a surrounding atmosphere. As such, heat will conform to certain fixed laws in its relations to the two bodies. It is always a definite fact that when two bodies in contact with each other are of different temperatures, they tend to become of equal temperature. The warmer will part with its heat to the cooler, and the latter will in like manner reduce the temperature of the former. By covering, then, the surface of the body, it is prevented from giving its heat directly to the air, for the clothes intercept it by absorbing the heat themselves.
In the second place the clothes prevent a too rapid escape of heat from the body, and by keeping a layer of warm air in contact with the skin, they preserve the body heat. Again, the various materials used to clothe the body vary much as to the readiness with which they conduct heat; accordingly we speak of good and bad conductors of heat. A bad conductor, such as wool, will keep the heat of the body from escaping to the air, and thus forms warm clothing, while a good conductor like cotton will lead away the heat quickly and prove cooler.
As said before, the texture of the material - that is, the size of its meshes - which allows air to pass more or less freely through it, also exercises a greater effect upon clothing. No healthy clothing is absolutely air-proof, the access of the air through it being necessary to our health and comfort. Thus oil-skin and mackintosh, which are air-tight as well as water-tight, make most people feel very uncomfortable.
In addition to their texture or permeability to air, and to their conducting or non-conducting powers, fabrics also vary according to their hygroscopic qualities. By hygroscopic is meant the power of absorbing moisture; thus a thin flannel is one of the coolest materials we can have, for it absorbs perspiration; while linen, which is non-hygroscopic, when moist allows the fluid to evaporate rapidly, and thus cools the body too quickly, and therefore dangerously. Hence flannel is a most suitable fabric in which to take exercise, as there is less danger of taking a chill.
There are four chief materials to be considered in connection with clothing, namely - cotton and linen, which belong to the vegetable kingdom, and silk and wool, which are obtained from the animal world. These four, either in their own form or else in combination with each other, such as merino, constitute most of our wearing apparel. Cotton is the fine, soft, downy material of a hairy nature which is found on the seeds of a certain plant, the cotton plant, which belongs to the mallow family. Its fibres are flattened in shape, and are twisted at intervals. The form of the fibres has an important effect in the action of cotton material on the skin. Being of a flattened shape, they have sharp edges, which in delicate skins are apt to cause irritation. Cotton wears well, it is not absorbent of moisture nearly to the same extent as linen, nor does it conduct away the heat of the body so quickly as the latter, hence it is a warmer material than linen. On the other hand, it does not retain the heat against the body like wool, and is an appropriate material for dress in hot climates. In merino there is a mixture of about one-fifth to one-half part of wool with cotton.
Linen, the other product of the vegetable kingdom, is obtained from the fibres of the common flax. Its fibres, unlike those of other fabrics, are distinguished by their roundness and their freedom from stiffness. These properties give to it that peculiar softness "which makes it so agreeable to the feel, and comforting and soothing to the skin. But, on the other hand, it has certain characters which are a drawback. As was stated before, it differs from cotton in that it is cooler, but unfortunately it absorbs moisture from the body quickly, and becomes saturated with perspiration. This is removed so quickly by the action of the external air, causing rapid evaporation, that there is great danger of a chill.