LODs and Collisions in Game Art: What They Are and How to Create Them in Blender and UE5

ByPropGon Academy

If you’ve ever imported an asset into Unreal Engine and the game ran slowly, or your characters walked through walls that should be solid, there are two concepts you need to master: LODs and Collisions. They’re invisible in the final game, but completely define whether your game runs at 120fps or 20fps.

What Are LODs (Level of Detail)?

LOD stands for Level of Detail. It’s a system where a 3D model is replaced by a lower-polygon version as the camera moves farther away. The player never notices, but the GPU renders millions fewer polygons per frame.

A typical LOD chain looks like this:

  • LOD0: Full-detail model (close range), e.g. 8,000 polys
  • LOD1: Simplified version, e.g. 4,000 polys
  • LOD2: Even simpler, e.g. 1,500 polys
  • LOD3: Very low poly, e.g. 400 polys
  • LOD4: Billboard / imposter (very far distance)

Why LODs Are Essential in Game Art

Modern game scenes have hundreds, sometimes thousands, of objects on screen simultaneously. Without LODs, a single distant bush with 5,000 polygons would be rendered at full quality even when it appears as a 5-pixel dot on screen. Multiply that by 500 bushes and your frame rate collapses.

LODs are not optional in professional game art, they are a fundamental requirement for any asset that will be placed in a scene.

How to Create LODs in Blender

The most common approach in Blender is using the Decimate modifier to create simplified versions of your mesh:

  1. Start with your LOD0 (full detail mesh)
  2. Duplicate it and apply a Decimate modifier at ~50% → this is LOD1
  3. Duplicate LOD1, apply Decimate at ~50% again → LOD2
  4. Repeat as needed for LOD3 and LOD4
  5. Export each LOD as a separate mesh, named SM_Prop_LOD0, SM_Prop_LOD1, etc.

Pro tip: For hero props (props that appear frequently or close to the player), create LODs manually rather than using automatic decimation, to preserve silhouette quality.

Setting Up LODs in Unreal Engine 5

Unreal Engine 5 can auto-detect LODs if you name your meshes correctly. When you import a static mesh:

  • Name your meshes SM_PropName_LOD0, SM_PropName_LOD1, etc.
  • In the FBX import dialog, enable “Import LODs”
  • UE5 will automatically build the LOD chain and assign screen size thresholds

You can fine-tune the screen size thresholds in the Static Mesh Editor under the LOD settings panel.

What Are Collisions?

Collisions are simplified invisible meshes that define the physical boundary of an object. The game engine uses them, not the visual mesh, to calculate physics, character movement, and projectile impacts.

Why not use the visual mesh directly? Because calculating physics against a 10,000-polygon mesh every frame is extremely expensive. A collision box with 6 faces does the same job at a fraction of the cost.

Collision Types in Unreal Engine 5

  • Simple Box/Sphere/Capsule: Auto-generated by UE5. Good for basic props.
  • UCX_ Collision (Custom): A hand-built collision mesh exported from Blender. The most precise and performant option for complex shapes.
  • Complex as Simple: Uses the visual mesh as the collision. Only for very small or static objects, never for dynamic props.

How to Create UCX Collisions in Blender

  1. Create a simplified mesh that approximates the shape of your prop
  2. Name it UCX_PropName_00 (Unreal requires the UCX_ prefix)
  3. Keep it convex, no holes, no concave shapes
  4. For complex shapes, use multiple UCX meshes: UCX_PropName_00, UCX_PropName_01, etc.
  5. Export it in the same FBX as the main mesh

Unreal Engine 5 will automatically detect meshes with the UCX_ prefix and use them as collision geometry.

LOD & Collision Checklist for Every Asset

  • ✅ LOD0–LOD3 created and named correctly
  • ✅ Polygon reduction ~50% per LOD step
  • ✅ UCX collision mesh created (convex)
  • ✅ Everything named with correct prefixes
  • ✅ Exported in a single FBX
  • ✅ LOD import enabled in UE5 import dialog
  • ✅ Screen size thresholds validated in Static Mesh Editor

Master LODs and collisions and your assets will go from “technically correct” to “production ready.” These are the two pillars that separate game art that ships from game art that crashes engines.

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