You can use a bitmap file or procedural map in the Opacity material component to make an object partially transparent. Lighter (higher-value) areas of the map render as opaque; darker areas render as transparent; and values in between are semi-transparent.

Click the Material Editor icon on the Main toolbar or press M. Click and hold the icon to show the flyout.

The gray levels of an opacity map determine the amount of opacity.
Setting the opacity map's Amount to 100 applies all of the map. Transparent areas are fully transparent. Setting the Amount to 0 is the equivalent of turning the map off. Intermediate Amount values are blended with the original Opacity value. Transparent areas of the map become more opaque.
Procedures
To use an Opacity map:
- Click the map button for Opacity.
3ds Max opens the Material/Map Browser.
- Choose from the list of map types, and then click OK.
(If you choose Bitmap as the map type, 3ds Max opens a file dialog that lets you choose the image file.)
- Use the map controls to set up the map.
Alternatively, you can use the
Slate Material Editor to
wire a map node to the Opacity component.