The thicker inner layer of the skin called

The thicker, inner-layer of the skin is called the Dermis. The thinner, outer-layer of the skin is called the Epidermis, that's the term for both of those layers. In the Epidermis, the tissue is different from the Dermis. The dermis contains a connective tissue. It's thicker, and gives strength to the skin mainly.  

Its simple its a because they are more fat