Thumbnails used by Toolkit apps (like the Loader) are stored in the local Toolkit cache to prevent unnecessary subsequent calls to the Shotgun server. While the default location should work for most users, it is configurable using the
cache_location core hook should you need to change it.
The default cache root location is:
Mac OS X
Thumbnails are stored per Project, Pipeline Configuration, and App (as needed). The structure beneath the root cache directory is as follows: