Files with the .CPGZ extension contain archives compressed using two methods – namely Copy In, Copy Out – CPIO for short - and gzip compression – also known as .GZ. It is similar to TGZ files, which use TAR archiving and GZ compression.

CPIO file compression is most commonly used in Unix systems - Mac OS and Linux. In both of these environments, you can use ditto commands in the command line of the system to create and extract CPGZ files. In Mac OS X, if, after an extraction attempt, a ZIP file changes to a CPGZ file, and the extracted CPGZ file is a ZIP archive, the loop may signify that the source file is corrupted and needs to be downloaded again.