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The Unreal Engine stores its assets in files known as packages. Packages can store different types of assets but are generally separated into the following types.

.ukx Animations
.uax Sounds – Not including Music
.utx Textures
.usx Static Meshes
.u Code
.rom Maps


.ukx packages contain a packaged .psk (mesh) and .psa (animation) files. On importing the mesh and animation files from ActorXporter (see Importing 3D assets for further details) the KFEditor creates an .ukx package. This package type contains animated assets; examples include but are not limited to: first person weapons, characters and moving props. Static Meshes

.usx packages are created from importing ASCII Export Files (.ase) into the KFEditor. Static meshes are 3D props that are commonly found around maps to add details. Examples include: stairs, railings, car wrecks, windows, scaffolding, weapon pickups, signs, trees and anything else you could imagine.


.uax packages take Waveform Audio File Format files (.wav) in either mono or stereo and up to a maximum resolution of 16bit 44.1kHz. Sounds in this format are commonly used for: Weapons, Foley, environment and characters (dialogue and effects).


.utx packages take 2D image files; accepted import formats include bitmaps (.bmp), portable network graphics (.png), Truevision TGA (.tga) and DirectDraw Surface (.dds) and create an .utx package.

Texture mapping is a method for adding detail, surface texture (a bitmap or raster image), or colour to a 3D model.


.u packages are compiled .uc files using UCC.exe, these UnrealScript classes compile into a single package. This could be a mutator, weapon, mod or entire game.


.rom is the file extention assigned for Unreal Maps. These are created and built in the Editor.

Package Naming

Generally there are some simple naming conventions users should try to follow when creating packages. Each package requires an unique name, for example if you had two packages, MyMod.ukx and MyMod.utx the engine would be unsure of which package it would need when MyMod called for. A simple yet effective way of naming packages involves the use of a suffix.

_A Animations
_S Sounds – Not including Music
_T Textures
_SM Static Meshes

This is just one example naming scheme. Now when the engine looks for MyMod_T it will not mistake it for MyMod_A