The clean image is a layer of directories and registry keys that provides isolation between containers and the host system. By default the foundation for a new container is the clean image.
All added programs on the host machine are fully isolated from the container. This includes elements like environment variables and other resources that may be included with the programs and applications installed on the host machine.
Containers leverage the host operating system by allowing read-only access of files and registry keys for these components from within a container.