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 degrees and 99 degrees 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 sir, and thus forms warm clothing, while a good conductor like cotton will lead away the heat quickly and prove cooler.