Fix: Unity Mesh Collider Convex Required for Rigidbody

Here is how to fix the “non-convex MeshCollider with non-kinematic Rigidbody is no longer supported” error in Unity. You imported a mesh, added a MeshCollider and a Rigidbody, and Unity throws this error. The object either falls through the floor, does not collide with anything, or the MeshCollider simply disables itself. This is a hard constraint from the PhysX engine and has no workaround — you must change your collider setup.

The Symptom

You have a GameObject with a MeshCollider and a non-kinematic Rigidbody. Unity logs the error: “Non-convex MeshCollider with non-kinematic Rigidbody is no longer supported in Unity X.X.” The collider is either ignored entirely or the Rigidbody behaves erratically. Objects clip through geometry, fall through floors, or produce no collision callbacks.

This error appears at runtime, not in the editor. In older Unity versions (pre-2019), this was silently allowed but caused unstable physics. Current versions explicitly reject the configuration.

What Causes This

PhysX requires all dynamic collision shapes to be convex. A convex shape is one where any line segment between two interior points stays entirely inside the shape — no indentations, holes, or concavities. Concave-to-concave collision detection is exponentially more expensive and numerically unstable in real-time simulation. Unity enforces this by requiring MeshColliders on dynamic Rigidbodies to have the Convex flag enabled.

The problem surfaces when you use a detailed game mesh (a spaceship, a character, a building) as a collider. These meshes are almost always concave. Enabling Convex on them produces a “shrink-wrap” approximation that fills in all the concavities, which often does not match the visual shape at all.

The Fix

Option 1: Enable Convex for simple shapes. If the mesh is roughly convex already (a barrel, a crate, a ball), just enable the Convex toggle. Unity will generate a convex hull with up to 255 triangles.

// Enable convex at runtime if needed
var meshCollider = GetComponent<MeshCollider>();
meshCollider.convex = true;

// Verify the cooking result
Debug.Log($"Convex: {meshCollider.convex}, Bounds: {meshCollider.bounds}");

Option 2: Use a compound collider. For complex shapes, approximate the mesh with child GameObjects containing primitive colliders. A spaceship might use a BoxCollider for the hull, two small BoxColliders for wings, and a CapsuleCollider for the nose. Unity treats all colliders in the Rigidbody’s hierarchy as a single compound shape:

// Structure in the hierarchy:
// Spaceship (Rigidbody, NO collider on this object)
//   Hull (BoxCollider)
//   LeftWing (BoxCollider)
//   RightWing (BoxCollider)
//   Nose (CapsuleCollider)

// The child objects should NOT have Rigidbodies.
// They inherit the parent Rigidbody automatically.
// Each child can be positioned/rotated to match the mesh shape.

Option 3: Use convex decomposition. For meshes that are too complex for manual compound colliders, use a convex decomposition tool like V-HACD. This breaks a concave mesh into multiple convex pieces automatically. Import the decomposed meshes and add a convex MeshCollider to each piece as a child of the Rigidbody:

// After V-HACD decomposition, you get multiple convex meshes
// Add each as a child with its own convex MeshCollider
foreach (Mesh piece in decomposedMeshes)
{
    var child = new GameObject("CollisionPiece");
    child.transform.SetParent(transform, false);
    var mc = child.AddComponent<MeshCollider>();
    mc.sharedMesh = piece;
    mc.convex = true;
}

“The golden rule: if it moves with physics, it must be convex. If it is scenery and never moves, it can be concave. If it moves but is script-driven, make it kinematic and keep it concave.”

Why This Works

PhysX’s collision detection algorithms (GJK and EPA) only work with convex shapes for dynamic objects. When you create a compound collider, PhysX treats each child collider as a separate convex shape that moves together. The collision is mathematically correct because each individual shape is convex, even though the combined shape they approximate is concave. This is the same approach AAA games use — no shipped game uses concave dynamic colliders.

Related Issues

If your MeshCollider is convex but the collision shape does not match the visual mesh closely enough, consider increasing the mesh resolution before cooking or switching to a compound collider. For trigger-only colliders that do not need physics response, see Fix: Unity AddForce Not Working on Rigidbody for kinematic trigger setups.

If your Rigidbody falls through the floor despite having a collider, check that continuous collision detection is enabled for fast-moving objects.

Dynamic means convex. Static means anything. Kinematic means anything. No exceptions.