Rendering materials are customizable. As you can see in the screenshot below, the rendering materials are split into Main and Sub Categories to categorize the materials for manageability. 

The material categories with the materials they contain are defined in the Rendering Template.xls file located in the Rendering folder that was previously downloaded and installed. 

After opening the Rendering Template.xls and starting with Sheet1 in the workbook, column A is specifying the Main Categories, Sub Categories are discussed on Sheet2. Notice the Microvellum Woods category in cell A1, the columns immediately to the right are specifying the Drawings that house the actual materials. In this example, the Microvellum Woods materials are spread out over several different Drawing files for manageability. The Sub Categories, material names, and previews are specified on corresponding Sheets. So the Main Category you want to add or modify will correspond with its row number + 1. So with the Microvellum Woods as an example, the Sub Categories and materials will be located on Sheet2. 

While viewing Sheet2, column A is specifying the Sub Category for the corresponding Main Category. The sheet has been color-coded to make it easier to see the relationship between the Sub Categories and the preview images. Looking at A1, which is Microvellum Featured Woods, the material previews are specified in columns B and C, where B is the material name, and C is the jpeg image for the preview. On the next Sub Category, Light Wood in cell A2, its corresponding columns are D and E, and so on for the remaining categories. 

Now that we have reviewed how the Microvellum Materials interface works let us add a couple of new categories and a material. We will start by locating Sheet1 in the workbook. For your reference, it will be easier to start with existing Material Categories, but in the example, we will start from scratch. Locate cell A49 and enter Wilsonart Laminate; this will be the main category for the materials. Next, we will need a drawing that will house the material. In this example, we will create a new drawing and assign it to our Wilsonart category. 

Starting with Drawing 1, type MATERIALS in the AutoCAD command line. When the Material Palette opens, select the Add Material button on the lower-left portion of the palette and choose New Generic Material. 

In this example, I located a Wilsonart Material called Typhoon Gold 4953 and have already downloaded the images off the Wilsonart website. The image needs to be placed in the Rendering folder, typically located in C:\Program Files\Microvellum\Toolbox\Rendering, under the Images and Image Preview folders. 

Now back in the Material Editor interface, click on the image filed on the palette and navigate to where the texture image is stored C:\Program Files\Microvellum\Toolbox\Rendering\Images and select the desired image, in this case, Typhoon Gold 4953.jpg. 

Next, you will need to go through the additional parameters below to achieve the desired look. See AutoDesk  for additional information available in the various topics from AutoDesk.com. You can click on Default Generic to change the name of the material in the current drawing. 

The jpeg image may require some adjustment to get the right look in the rendering by adjusting the Sample Size. 

Now exit out of the Materials Editor and close the Material Palette. Save the drawing to the Rendering folder under Drawings. 

Now that we have created a new drawing and material, we can finish setting up the Rendering Template.xls file. From where we left off, we need to assign the drawing that houses the new material, so in cell B49, we will enter the drawing name, Wilsonart Laminates.dwg. 

Now, locate the corresponding Sheet on Sheet50. We will create a new Subcategory called New Designs in cell A1. Now we will add the material name and preview image. 

Now close and save the file, if you get a compatibility message from Excel, just hit the Continue button to save the file. Now open the Microvellum Materials, and the new Main and Sub Categories will be available along with the new material for rendering.