It is Styrofoam or polystyrene which is largely used as food containers for vegetables and fishes.

Dirt can easily be trapped into the tiny gaps between polystyrene particles, especially the containers are pulled on wet floors in markets.

The SBSAR file allows you to change the colors of the Styrofoam and dirt. The dirt level can also be tweaked.

This material is a polystyrene which is as known as Styrofoam in the US. It is an excellent insulation, so it is commonly used as a takeaway food containers.

If you want to fine tune the color, e.g. making it more yellowish or greyish, the SBSAR file may help.

It is a foam board or technically, polystyrene material. The pattern of monomer can be found on the surface of this synthetic aromatic hydrocarbon polymer.