Materials simulate various effects such as reflections and textures. You specify the render appearance for each material using the Materials dialog.
When the rendering engine renders materials, its performance depends on the effects being simulated. In fact, complicated render appearances for materials can slow down the rendering process more than complicated geometry in the building model.
When preparing to render an image using the Revit rendering tool, consider the following.
The complexity and size of a color or pattern affect render speed. More complex patterns require the rendering engine to calculate more samples so it can capture the details. The rendering engine works best when it can identify areas of similar surface treatment and can estimate appearances over large homogeneous areas.
For example, a smooth monochrome surface renders more quickly than a smooth patterned surface. A large-scale pattern renders more quickly than a dense, intricate pattern. A detailed, perforated surface renders more slowly than a simple surface.
The render appearance of a material specifies its reflectivity. Revit can render matte reflections quickly. However, any material characteristic that causes visual distortions (such as blurred reflections or transparencies) requires more work to render, and so requires more render time.
Shiny and mirrored reflections are slightly more difficult to render than matte reflections. A fritted surface is more difficult to render than a smooth, glossy surface. Water is more difficult to render than glass. Metal with a patina or a hammered surface is more difficult to render than polished metal.
Blurred reflections are the most difficult to calculate.
Refractive materials, like glass, usually involve reflections as well. As a result, these materials are more expensive (in time and resources) to render than others. Also, the average pane of glass has 2 layers or sides, requiring multiple layers of refraction. When rendering an image, all of the layers must be calculated so you can see through the glass. For example, you need at least 6 refractions to see through 3 panes of solid glass.