Second skin

The concept of a second skin is common to a range of clothing-related fetishes.

One reason why these materials may be fetishised is that the garment acts as a fetishistic surrogate for the wearer's own skin -- a second skin. The material may be regarded as providing a super-stimulus that is more intense than the normal response associated with real skin.

The forms of fetishism related to this concept can be regarded as forming a spectrum, as follows:

Spandex fetishism (shiny, smooth, soft, porous)
Rubber fetishism (shiny, smooth, less yielding, waterproof)
Leather fetishism (shiny, smooth, waterproof, material of animal origins)
Fur fetishism (soft, warm, material of animal origins)

Somee examples of turn-ons that are related to these:

In spandex fetishism, wearers of skin-tight spandex garments may be perceived by the viewer as being naked, or simply coated in a shiny substance like paint. Many of the stretch fabrics are also shiny and often produced in bright colours, adding further visual stimulus to add to the physical sensations produced by the material. The tightness of the garments may also be viewed as a kind of bondage.
In rubber fetishism, as above, but with the additional smell and less yielding nature of rubber. The association with sex toys is also significant.
In leather fetishism, as above, but with the added association of animal skin, and the association of "rugged" leather-wearing lifestyles, and leather bondage equipment.
In fur fetishism, the fact that the fur was originally an animal's skin and hair, and that it provides warmth and comfort. There is also an element of atavism involving associations with the nature of the animal.

The title of the fetishistic magazine "Skin Two" alludes to this concept.