The ability to transmit water' vapor is one of the important properties of leather that makes it so desirable for use in the construction of shoes. Knowledge of the factors involved in this property is, therefore, important in the proper selection and manufacture of materials that will give improved service and yet maintain a sufficiently high level of water vapor permeability to assure comfort to the wearer.

The water vapor permeability of leather is inherently high. However, the use of fats and greases to improve water resistance of shoe leather may lower water vapor transmission to the point below the critical level, which has not been determined, at which the foot may be comfortable under a particular set of temperature and humidity conditions which the wearer of the shoes may encounter. It would be desirable to maintain water vapor transmission at a high level while simultaneously liquid water transmission is maintained at a low level. The purpose of the present investigation was to study the mechanism of water vapor transmission.