Why does importing FBX files take so long in Unreal compared to Blender

Development World Creation
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Hey everyone

I try to import some FBX files into Unreal and I notice something weird. Not talking about textures or materials here everything is fine with that. The problem is the time it takes to import. If I take the same FBX file and open it in Blender it loads in one minute (its a single 2Gb file with many props in it). But in Unreal it takes two or three hours sometimes. I don’t really know why this happens. It happens all the time with different files. In Blender It opens all the assets rights away in the viewport and places them in the outliner. In Unreal it takes forever to load those assets in content browser..

Is this normal or maybe I need to change something in the settings when importing the FBX to unreal. If anyone has tips to make this faster I would really be grateful for.

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I find that if you import the FBXs into a blueprint or as a level, it goes faster (and they are not only placed in content browser)

  1. Create a new empty level
  2. Create a designated folder for where to store the mesh/materials/textures etc for the import.
  3. Go to File → Import into Level
  4. Chose what to import
  5. Select folder location for the imported mesh and select OK.
  6. Scene → Import Options → Hierarchy Type → Create on Blueprint asset (or chose one of the others types)
  7. Change the settings you want
  8. Import
  9. When its done importing, the blueprint will open up.
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Some of the import settings will greatly increase the import time, turn off anything that says build/generate/remove/etc, basically turn off anything that adds overheard and keep the settings that import things like normals and tangents. Should be 20x faster to import on those large meshes.

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While I’ve never encountered a 2-3 hour import, there are a lot of reasons Unreal imports can take so much time, like @ZacD said.

Some of those features that increase import time (static mesh):

  • Generate missing collisions (necessary for any gameplay mesh, also very time consuming, per-mesh)

-Remove Degenerates (mesh tool to remove bad triangles. Necessary to keep if not using Nanite, per-tri)

-Build Reversed Index Buffer (from my understanding, only needed for mirroring meshes, can probably turn this off, per-vertex)

-Generate Lightmap UVs (not needed for Lumen lighting, this is only for baking your lighting, per mesh)

-Transform Vertex to Absolute (no reason to disable this, per-vertex)

-Compute Weighted Normals (better for more accurate lighting, per-vertex)

-Convert Scene (should be a quick process, also necessary, per-mesh)

-Material Import Method (if creating materials, needs to internally open the material creation logic, create a material, import the textures, add them to the material, then save that new material. This is done per-material index and can be very slow)

-Reorder Material to Fbx Order (should be really quick, per-material index)

Honestly, the collision generation and material creation are probably what’s taking the most time. 2GB is a pretty big asset for game design, and it sounds like you’re trying to import a lot of assets at once. Keep in mind that Blender is made to open FBX files, whereas Unreal is more of meant to read the FBX files and convert the found components into game assets.

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Thanks guys for your Help.

@Sarahlenker , yeah your right, the fbx is basically just a collection of assets. I ended up ditching the idea of importing the whole thing, even after disabling some features. Still took too long and honestly not worth the wait. btw the material part, yeah I noticed that really helped reduce the time.

anyways what I ended up doing is opening the fbx in Blender and just sending over what I actually need using the Send to Unreal add-on. in case you’re interested the official one isn’t being updated anymore but there’s a forked version that’s pretty stable. tested it with UE 5.4 and Blender 4.4, works great.

so yeah I just transfer to Unreal the asset I need. the cool thing is I can send them as a whole block if I group the assets under an empty parent (which in my case the assets already come with) then tweak the add-on settings to get that into Unreal as one unit. super useful when I wanna keep the full structure without breaking everything into parts.. and then yeah I also import the sub assets I need to build that block if needed. so basically I bring in both the grouped version and the separate pieces. gives me options depending on the use case.

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