In Cinema 4d you can assign more than one material to a single object. For this example I’m going to use a simple polygon object.

First I’m going to select the faces I want to assign the first texture to.

Then go to Selection, and Set Selection. Go ahead and give it a name, then deselect the object before making the next selection.

You’ll notice that a triangle appears to represent that selection.
Now select the other set of polygon faces, then go back to Selection, and Set Selection. Now the other half of the polygons are selected. Go ahead and name that selection as well.

Now create two new materials.

Then double click on the triangle icon to select the first selection of polygons...

Then right click and select “Apply”

Now that set of polygons have the material applied to them.

