United States Bureau of Reclamation set four main requirements to be satisfied by a filter material for it to be considered as a protective filter.

In protective filter, each subsequent layer becomes increasingly coarser than the previous one, and hence, it is also called a reverse filter or inverted filter.

As per the criteria given by Terzaghi, the grain size curve of the material should be roughly parallel to that of the base materials.

The D15 size of filter material must not be more than 4 to 5 times D85 size of the base materials. This prevents the foundation materials from passing through the pores of the filter material.

The filter material should be sufficiently coarse and pervious so that the incoming force is rapidly removed without any appreciable buildup of seepage forces within the filter.

A protective filter designed in such a manner as to provide quick drainage, yet prevent the movement of soil particles.

A protective filter consists of a combination of layers of pervious materials to provide quick drainage.

With a proper drainage filter under slope or rock fill toe, the phreatic line in an earth dam can be kept well within the body of the dam.

Weighting filters at the bottom of drainage sumps and trenches arrest the percolating water at the exit and allow its safe exit without inducing piping.

The soil to be protected i.e., the embankment or foundation material surrounding the filter is known as the base materials.