Filtillägg börjar med tecknet "U"
| FILTYP | Kategori | Filformat | |
|---|---|---|---|
| .u3i | Text Files | U3 Application Information Fil | |
| .ubj | Data Files | Universal Binary JSON File | |
| .uccapilog | Microsoft Files | Microsoft UCC API loggfil | |
| .ud | Data Files | OmniPage Egen ordlista | |
| .udc | Data Files | Adobe InDesign Egen ordlista | |
| .udeb | Data Files | Debian Paketfil | |
| .uds | Data Files | Sierra Generationer Fil | |
| .uea | Data Files | Protector Suite QL Krypterad Arkiv | |
| .uha | Archive Files | UHarc Komprimerad Arkiv | |
| .uhtml | HTML Files | UC Browser sparade webbsida | |
| .uibak | Backup Files | UltraISO Backup skivavbild | |
| .uif | Disk Image Files | Universal Bildformat Skivimage | |
| .ulf | Data Files | Universell List File | |
| .ulz | Data Files | USBlyzer Data Capture File | |
| .umf | Data Files | MediaHolder Universal Media Format File | |
| .unauth | Text Files | SiteMinder Obehörig meddelandefil | |
| .unity3d | Game Files | Unity Web Player fil | |
| .unitypackage | Package Files | Unity Paketfil | |
| .unl | Multiple Use Files | Garmin Lås fil | |
| .unx | Text Files | Unix textfil | |
| .uoml | Text Files | Unstructed Operation Markup Language File | |
| .upd | Text Files | Program Update Information | |
| .update | Data Files | ISAPI Uppdatera Arkiv | |
| .upg | Multiple Use Files | Uppgraderingsfilen | |
| .upk | Game Files | Unreal Engine 3 paket | |
| .upr | Data Files | Fractal Parametrar File | |
| .url | Web Files | Internet-genväg | |
| .usm | Digital Video Files | USM Game videofil | |
| .ustar | Data Files | Enhetlig standard bandarkiv Format File | |
| .utf8 | Text Files | Unicode UTF8-kodad text dokument | |
| .utxt | Text Files | Unicode textfil | |
| .uvf | Data Files | Osäkert värde Format | |
| .uwl | Data Files | Användar Word List File | |
| .uzip | Disk Image Files | FreeBSD komprimerad skivavbild |