/var/cache/distfiles
From Gentoo Wiki
/var/cache/distfiles is the default directory Portage uses to store source code files. These are typically in a compressed package format. Portage defines this default value in /usr/share/portage/config/make.globals, and this directory definition can be altered by changing the value of the DISTDIR variable in make.conf.
See also
- Eclean — a tool for cleaning repository source files and binary packages.