OBB Expansion Files Internals
Also known as: obb file android, expansion file storage, android obb files, opaque binary blob
OBB (Opaque Binary Blob) expansion files are large asset bundles, mainly game data, stored alongside an Android app outside its APK. They live under Android/obb/<package>/ on shared storage and let titles ship gigabytes of media beyond installer size limits.
- Stored under Android/obb/<package>/ on shared storage, separate from the APK.
- Hold large read-only game assets and are often ZIP-format archives.
- Auto-removed on uninstall but can occupy gigabytes while installed.
What OBB files are
An OBB (Opaque Binary Blob) is an expansion container that holds an app's bulky read-only assets, typically textures, audio, and video for games, separately from the APK. Historically they let developers exceed Google Play's APK size limit by attaching a main and optional patch expansion file per app.
Physically they are stored at /storage/emulated/0/Android/obb/<package>/, often as a single large file with a name like main.<versionCode>.<package>.obb. The format is commonly a ZIP-style archive the app mounts or reads at runtime; it is 'opaque' because the platform does not interpret its contents.
Why cleaners flag them
Modern apps increasingly use Play Asset Delivery and split APKs/AAB bundles instead of classic OBBs, but many installed games still carry multi-gigabyte OBB data. Because it sits in the app-owned android-data-folder sibling Android/obb/, it is auto-removed on uninstall but otherwise persists and dominates a device's storage report.
Storage cleaners surface these as some of the largest single items on a phone. A large files finder will list big OBBs so users can see that a single game is consuming gigabytes, and decide whether to keep or remove the title rather than chase small caches.