Material design is a new standard in design encouraging precise design practices and logical animations. The simplicity of the design is underlined by the precision of a classic design grid-like balanced approach.

Paper Elements has defined the original look of  Material Design in Android and Chrome Applications. the style of design use very strong lines and block like forms. 

Paper Elements within a Material Design structure give clear defined parameters , where shadows and clean animations are used to provide a sense of structure.

The sharp almost flat looking design approach leads your eye throughout the page without any distraction. The important key is that the precision of element using the shadow is actually a depth z axis which intuitively looks correct to the eye and the overall dimension proportions of a page.  

A Paper Elements Example - Paper Shadow

A simple depth describes the z axis. You can organically describe an Applications Priority  simply but manipulating the z axis and creating the natural shadowing.