The waterproofness of the leather is the reduction of the water absorption and water permeation properties of the leather in various proportions. This ratio differs from decreasing the water absorption of the leather to a certain extent until it loses its wetting property. In the processes which are given waterproofness to the leather, it is tried to provide continuous and sufficient waterproofing activity in the whole area of ​​the skin by using auxiliary materials. However, while the leather is waterproof, the air and water vapor permeability of the leather should be preserved.

The effect of water against the skin is in three ways. The first is water retention of the skin surface. The second is the penetration of water into the fiber structure of the skin. The third is the wetting of the skin with water ingress. All three properties are related to the surface tension of the skin. Auxiliary materials that reduce surface tension facilitate wetting. If a high percentage of leather is desired to be impervious to water, it is necessary to use tight-structured raw leather.

Emulsifiers used in leather processing stages are highly effective in water permeability. The wetting effect of nonionic emulsifiers is significantly low. Washing of the salts before the skin is dried also reduces wetting.

The materials used in the waterproofing processes are those which lubricate the surface of the skin, soften the skin and significantly prevent the skin from absorbing water. In fact, under normal conditions, the structure has the property of absorbing water. In order to retain the skin and maintain its form, its water absorption property must be limited.

Tests are carried out by local and foreign accredited laboratories accredited laboratories to determine the sensitivity of the skin to water within the scope of specific tests. In these tests, national and international standards are taken into consideration. Standards for determining water fastness to the skin are as follows:

• TS EN ISO 11642 Leather - Color fastness tests - Color fastness to water

This standard specifies a method for determining the color fastness of the skin to water during the processing of any kind of leather.