Collisions Not Working in Blender: Top Fixes and Expert Tips

When you’re building a 3D scene in Blender, nothing is more frustrating than collisions not working as expected. Maybe your objects fall through the floor, or two meshes pass right through each other. If you’ve spent hours setting up your scene, it can feel like Blender is broken. But most of the time, there’s a clear reason—and a solution.

Let’s look at why collision problems happen in Blender, how to fix them, and some practical tips to save you from hours of frustration.

Why Collisions Matter In Blender

Collisions are a key part of physics simulations. Whether you’re making a bouncing ball, a character walking, or a cloth draping over a table, you need Blender to know that objects should not pass through each other. Without working collisions, your animation or simulation will look unrealistic.

Blender uses physics engines to calculate these interactions. But even one small setting can stop everything from working. Understanding the most common causes can help you avoid wasted time.

Common Reasons Collisions Fail

Here are the main reasons why collisions do not work in Blender:

1. Missing Collision Physics

You must add a Collision or Rigid Body modifier to each object that should interact. If you forget, Blender ignores that object in simulations.

2. Incorrect Object Types

Soft bodies, rigid bodies, and cloth have different settings. If you mix them incorrectly, collisions can break.

3. Scale Issues

If your object is too small or too large, the physics engine might not detect collisions. Always apply scale (Ctrl + A > Apply Scale).

4. Simulation Order

Sometimes the order of modifiers or the baking order causes issues. Re-bake the simulation after any change.

5. Normals Facing Wrong Way

If mesh normals point inward instead of outward, Blender can’t calculate the surface properly.

6. Collision Margin Too Small/large

A margin that’s set too high or too low can stop collisions from working.

7. Subdivision Surface Modifier

If you add Subdivision after Collision, Blender uses the wrong mesh for physics.

8. Disabled During Rendering

Sometimes collisions are set for viewport, but not for rendering.

Credit: blenderartists.org

Quick Troubleshooting Checklist

Before you dive into more complex solutions, try these simple steps:

• Select each object and check the Physics Properties panel.
• Apply scale and rotation to all objects.
• Make sure the collision modifier is before the subdivision surface in the stack.
• Check if the simulation is baked after changes.
• Flip the normals if the mesh behaves strangely.

Often, just following this checklist solves most basic collision problems.

Blender Physics Types: How They Affect Collisions

Blender offers several physics types. Here’s how they compare for collision handling:

Physics Type	Collision Support	Common Use
Rigid Body	Excellent	Falling objects, dominoes
Soft Body	Good (with tweaks)	Jelly, bouncing balls
Cloth	Very good	Clothes, flags
Fluid	Specialized	Water, smoke

Insight: Sometimes, users try to simulate a bouncing ball using only Soft Body, but Rigid Body is more reliable for hard collisions.

Collision Settings Explained

Each collision-enabled object has several important settings:

• Thickness: How far the physics engine keeps objects apart.
• Friction: How much objects slow down when touching.
• Margin: The invisible buffer for detecting collisions.

Getting the numbers right is important. For example, if the margin is too small, objects can pass through each other at high speed.

Here’s a comparison of default versus custom settings:

Setting	Default Value	Recommended Range
Margin	0.04	0.02 – 0.06
Friction	0.5	0.3 – 0.7
Bounciness	0	0 – 1

Small adjustments here can make a big difference in results.

Steps To Fix Collision Problems

If you’re still stuck, follow these practical steps:

1. Apply Transformations

Select your object, then use Ctrl + A to apply scale and rotation.

2. Check Modifier Order

In the modifier stack, Collision should come before Subdivision Surface.

3. Bake The Simulation Again

Every time you change settings, re-bake. Old bakes can cause objects to ignore new settings.

4. Check Normals

Enter Edit Mode (Tab), select all faces (A), and use Shift + N to recalculate normals.

5. Adjust Collision Margins

Try increasing the margin slightly if objects still pass through each other.

6. Test With Simple Shapes

Replace your mesh with a simple cube or sphere to see if collisions work. If they do, the problem may be with your object’s geometry.

Advanced Tips Most Beginners Miss

• Apply All Transforms Before Adding Physics:

If you add Rigid Body or Collision before applying scale, Blender uses the old dimensions. This often breaks collision detection.

• Use Simple Collision Shapes:

For performance, set collision shape to Box, Sphere, or Capsule if possible. Complex shapes (Mesh) are slower and sometimes unreliable.

• Simulation Substeps:

In Rigid Body World settings, increase substeps per frame if objects are moving fast. This gives more accurate results and prevents objects from tunneling through each other.

• Non-Manifold Geometry:

Holes or non-manifold edges in your mesh can break collision. Use Mesh > Clean Up > Make Manifold.

Real-world Example

Suppose you have a ball that falls through the floor in your Blender animation. You check and see:

• The ball has a Rigid Body modifier, but the floor does not.
• The floor’s normals point down instead of up.

To fix it:

• Add a Rigid Body or Collision modifier to the floor.
• Recalculate the floor’s normals to face upward.
• Apply scale to both objects.
• Bake the simulation again.

Now, the ball bounces as expected.

Credit: blender.stackexchange.com

When Collisions Still Don’t Work

Sometimes, even after all these steps, collisions still fail. This usually means:

• The mesh is very complex or broken.
• There’s a bug in Blender (rare, but possible).
• Add-ons or custom scripts are interfering.

In these cases, try:

• Exporting your objects and importing them into a new scene.
• Simplifying the mesh.
• Checking Blender’s official documentation or community forums for updates. The Blender Manual is a good resource.

Frequently Asked Questions

Why Do Objects Fall Through The Floor In Blender?

This usually happens when the floor doesn’t have a collision modifier or Rigid Body. Also, check if the floor’s normals are facing the right way and that you applied the scale.

Do I Need To Bake The Simulation Every Time?

Yes. Every time you change physics settings, collision, or modifiers, you should bake again. Otherwise, Blender uses old data, and new collisions won’t work.

How Do I Fix Collision Issues With Cloth Or Soft Body?

Check that both the cloth and the object it should collide with have the correct collision settings. Also, increase the collision quality and margin slightly for better results.

Can Scale Affect Collisions?

Absolutely. If you scale an object in Object Mode but do not apply the scale, Blender’s physics engine uses the wrong size. Always apply scale (Ctrl + A) before adding physics.

What’s The Best Collision Shape For Complex Models?

If possible, use simple shapes like Box or Capsule for collision. For very complex models, use Mesh, but be aware it’s slower and less reliable.

Fixing collision problems in Blender can be tricky, but with the right steps, it’s almost always possible. With a little patience, you’ll get your simulation working smoothly and avoid the common mistakes that trip up most beginners.

Credit: forums.unrealengine.com