The first file that we’re going to look at is the [Content_Types].xml file, and this is the file that confirms that the ZipPackage class is used. There’s an article here that is ten years old but is still valid (scroll down to the System.IO.Packaging INcludes Zip Support to read up on this.) This is because we know that the content_types file is part of the output when using the ZipPackage class to zip up a bunch of files into a .zip. The content_file contains both the extension and content type of the three other files that are included in the ispac:
Note that the content_types file does not specify the files, either in quantity or in content, other than the fact that they will contain xml.
Read on for a good amount of detail on what’s included in an Integration Services package.