Smoke objects are defined as an environmental object, they can be positioned and adjusted to not only look like smoke but fog or haze to.

Smoke objects are created by selecting the Smoke tool.

After selecting the tool click, hold and drag in the scene window, and a smoke object will grow until the mouse button is released. The Smoke object will remain looking like a wireframe no matter what Display mode the scene is in. That is because it is an environmental object and consist of no polygons.

After creating the Smoke object it will appear on the Project List. Next to it's name will be a properties icon, a hide and ghost button, it will also have a keyframe which means it and all of it's properties can be animated.

Like other objects, Smoke can be manipulated using the Object XForm tools.

But the whole radius of a Smoke Objects is all that can be scaled. Even if the Scale tool is set to only scale along a single axis the whole Smoke object will be scaled evenly.

Setting up the characteristics of Smoke objects is done on it's Properties Menu. The Properties Menu can be found the same as other objects by clicking on the icon or right clicking on the object itself or it's name.
The Position & Radius tab can be used to position the smoke numerically using the Position options or size it using the Radius option.

The Smoke tab has four option for setting up how the smoke will appear at any selected keyframe.

The Color option has the three color pallet ( system, program & numeric )

The Density option sets how thin or thick the smoke appears. With lower values being thinner and higher values being thicker. Drag the slider to set it.

The Frequency option breaks the smoke up or makes it appear more or less choppy. With higher values broken up more and lower values compacted together more. Values are typed in and can range from 0.000 to 1000.000

The Contrast option determines how the empty spaces or gaps in the smoke will appear. With lower values filling in the gaps more and higher values separating them.This is a good option to use when animating, when you want the smoke not to change drastically but yet have settle movement.

As you can see from the above images drastic values in any option can make the Smoke appear solid. It is a combination of these options that will help give a desired effect.

The Render tab has properties which determines how the Smoke will be rendered. These options can not be keyframed for animation.

The Shadow option lets the Smoke receive shadows. The render shadows option on the Radiocity menu will also have to be enabled for shadows to be rendered in the scene. Smoke objects cannot cast shadows.

Number of Samples option determines the dimensional look of the Smoke. With lower values looking more 2D and larger values appearing 3D. This option basically sets the number of layers the smoke will have, lower numbers will speed up the render but the Smoke will look flat and the layers may be visible. Higher numbers will increase the render time but give the Smoke more depth.

Random Sampling sets the amount of noise rendered in to the smoke. Values here can be set between 0.000 and 1.000, larger values give a more natural appearance.

The Info tab, shows the polygon and range information, as can bee seen Smoke objects have no polygons.

Below of some examples of various smoke settings. The formulas for each image are listed.