Autodesk Combustion has an extremely powerful tool – 3D fog for simulating and rendering realistic fog in your compositions. But 3D fog uses a Z-Depth which is usually obtained from 3D software packages like Maya or 3D Max while rendering. What if you working on 2D composite and need finish it quickly. To speed up things you can use pre-made fog footage. So whenever you want to composite fog onto footage, you can just make use of this footage.