Render in AutoCAD: assign materials to 3D objects with the Materials Browser or by layer, then output an image with RENDER

A 3D model in AutoCAD is, by default, a set of grey solids. To get a view with brick or concrete faces for a client or a design report, you need two steps: assign materials to the objects, then render an image. To render in AutoCAD you need no outside software; everything is built in.

This article goes through both steps in AutoCAD 2027 with the acadiso.dwt template, on a 1 000 × 600 × 400 box and a 1 000 × 200 × 1 500 wall. Modelling solids is covered in 3D solids in AutoCAD. For drafting taught properly, the Institute runs an AutoCAD course for construction.

Starting the commands

Aliases and locations come from the 2027 acad.pgp and acad.cuix files. The Autodesk documentation on RENDER is the official reference page for the command.

Which materials a new drawing has

A new drawing from acadiso.dwt lists only three entries: ByBlock, ByLayer and Global. The first two are ways of assigning; only Global is an actual material.

So a new box takes its material from its layer, and layer 0 carries Global. For brick or concrete you have to bring a material in from the library.

The Materials Browser: the built-in library

Type MAT. The Materials Browser opens and MATBROWSERSTATE changes from 0 to 1. The lower part is the Autodesk library, grouped by category; the Masonry: Brick category, for example, holds materials such as 12in Running - Burgundy and 12in Uniform Running - Gray.

Each library material shows three lines of information:

Right-click a library material and the menu has four items: Assign to Selection, Rename, Delete and Add to. Add to opens a submenu: Document Materials, Favorites, Active Tool Palette.

The name comes into the drawing unchanged, and it is the name you must type character for character, spaces and hyphens included, when assigning a material to a layer from the command line. Close the browser with MATBROWSERCLOSE; MATBROWSERSTATE returns to 0.

Assign materials in AutoCAD: select the objects first

The quickest way is to select the objects first, then right-click the material and choose Assign to Selection.

Select the box and assign 12in Running - Burgundy, and two things happen at once. The material is copied into the drawing: the list now has 12in Running - Burgundy alongside the original three. And the box's Material property changes from ByLayer to 12in Running - Burgundy.

To bring a material into the drawing for later without assigning it, choose Add to → Document Materials. The material joins the drawing's list but is not yet on any object.

Assigning materials by layer

In a large model, assigning by layer is tidier: if every wall is on layer TUONG, you assign the material once, to the layer. Use -LAYER and its MATerial option, which sits in the main option list between TRansparency and Plot:

Enter material name or [?] <Global>: 12in Uniform Running - Gray
Enter name list of layer(s) for material "12in Uniform Running - Gray" <0>: TUONG

The second prompt's default in angle brackets is the current layer, 0 here. Read it before pressing Enter: an empty answer puts the material on layer 0 rather than on the layer you meant.

Layer TUONG now carries 12in Uniform Running - Gray. Draw a wall on that layer and its Material property is ByLayer; in the render, the wall shows the layer's grey brick.

The two methods side by side in one drawing:

This option accepts only materials already in the drawing. Type a name that is not there and AutoCAD reports it and asks again:

Enter material name or [?] <Global>: KhongCo
Cannot find material "KhongCo".

Type ? to list them: in a new drawing the list holds only Global. So bring the material into the drawing with the Materials Browser first (Add to → Document Materials), then assign it to the layer. Layers in general are covered in layers in AutoCAD.

The render command in AutoCAD: -RENDER step by step

RENDER opens the render window with the current settings. The command-line version -RENDER asks for each setting in turn, which is handy for saving an image to a file:

Specify render preset [Low/Medium/High/Coffee-Break/lUnch/Overnight/cuStom] <Medium>: M
Specify render destination [Render window/Viewport] <Render window>: R
Enter output width <800>: 800
Enter output height <600>: 600
Save rendering to a file? [Yes/No] <No>: Y
Specify output file name and path: c:/t9/render-M.png

The second question picks where the image appears: Render window or Viewport. With Viewport, AutoCAD asks neither for a size nor for a file; it renders straight away and reports Render Complete. To get an image file, choose Render window as above.

The defaults are Medium, 800 × 600, and no file. You must answer Y to Save rendering to a file? to get an image file. The file comes out at exactly 800 × 600 pixels. The render window stays open after the file is written, and its title bar shows the file name, for example c:/t9/render-H.png (Zoom 100%) - Render, so you can tell which image you are looking at. When you are done, RENDERWINDOWCLOSE closes the render window.

Render 3D in AutoCAD: Low, Medium or High

Same two-solid scene, same 800 × 600 size, three presets:

Low was the first render of the session and Medium the second, which is worth keeping in mind when reading the two short times: they are too close to rank the presets. All three files are exactly 800 × 600. The High file is the smallest, about 23% smaller than the Low one, so file size is no measure of image quality.

The big jump is High: from seconds to nearly ten minutes for a scene of just two solids. Side by side, the brick faces at High are smoother and less speckled, but at 800 × 600 you have to look closely to see it.

Work in that order: try views and materials at Low or Medium for speed, and run High only for the final image once you are happy. The default render background is black, as in the image at the top.

A short workflow for one presentation view

1. Model the solids and put walls and slabs on their own layers.
2. MAT opens the Materials Browser.
3. For layers: Add to → Document Materials, then -LAYER → MATerial to assign each layer.
4. For individual objects: select them, then Assign to Selection.
5. Pick a view, for example -VIEW → SEISO.
6. -RENDER, preset M, answer Y to save, type a .png name.
7. Once you are happy, run it again at H.
8. RENDERWINDOWCLOSE and MATBROWSERCLOSE to tidy the screen.

To send the 2D drawing itself as a file, use the method in saving AutoCAD as PDF.

Three things often repeated that are not true

Frequently asked questions

Do I need other software to render in AutoCAD?

No. The Materials Browser and RENDER are built in. Assign materials, then -RENDER to a PNG file.

How do I assign materials to 3D objects?

Type MAT, select the objects, right-click a library material and choose Assign to Selection. Or assign to a layer with -LAYER → MATerial.

Why is Assign to Selection greyed out?

Because nothing is selected. Select the objects first, then right-click again.

Which preset should I use?

Low or Medium to try things out, in seconds. High for the final image, but a two-solid scene at 800 × 600 took about 9.5 minutes.

When does a library material become part of the drawing?

Once it is assigned to at least one object with Assign to Selection, or added with Add to → Document Materials. Just opening the Materials Browser leaves the drawing's list at ByBlock, ByLayer, Global.

I rendered but there is no image file.

In -RENDER, Save rendering to a file? defaults to No. Answer Y and type a file path.