The Windows Installer Folders are a subset of Windows Installer Properties. They cover folders like the Windows folder, Program Files, Temp, etc.
These folders are very useful for specifying paths on the target computer. Regular paths (like C:\ or C:\Program Files) don't make sense any more, as the Program Files folder may be on a different drive and have a different name on other computers. Instead you must use Windows Installer folders like [WindowsVolume] or [ProgramFilesFolder].
The values of the Windows Installer Folder properties always end with a path separator (the backslash character). On the other hand, the values of the user-defined folder properties are not guaranteed to end in a path separator until after the CostFinalize Standard Action has run. Therefore, make sure that you are not including a path separator explicitly in a path Formatted Type string if the directory property you are using already includes one.
In this case you would use:
For more details about Windows Installer folder properties see: