Material Layering is a new way of mixing materials in a stack, which allows you to generate the correct material graph with no need to create the node graph by hand.
Passing Parameters to Layers
There are three main methods at present to do this, most of which apply to Blends and Layers.
The parameters listed will be available for use within your Material Graphs. There are two parts to using the system. The first is setting the shared inputs, which should generally be done at the top-level Material Graph. Continuing with the example collection, the inputs are hooked up to parameters in this case but could be any material graph nodes:The parameters listed As the parameters here are connected from the main Material Graph, they will be listed in the Material’s Global Parameters list when editing a Material Instance. In this respect, the parameters will be shared between any other graphs that read from them.
Of note, the Get Shared Input node in the graph above lists as a Texture2D input. This type is set if the parameter is found but will list an unknown type error if the parameter no longer exists. There is no system in place at this time to automatically rename parameters for you. In a future release, this may be implemented or the Name entry box replaced with a drop-down list of available parameters.
Tim Hobson, Epic Games
The guide was originally published here.