The best way to add collision to a Unity asset 3D model is to use Unity’s built-in collider components tailored to the model’s geometry and performance needs.
Colliders define a model’s physical boundary for interactions like collisions or triggers: Box Collider for rectangular shapes, Sphere Collider for rounded objects, and Mesh Collider for complex meshes (though it’s less performant). For detailed models, combine simple colliders into a Compound Collider—this balances collision accuracy with smooth performance.
If your model is high-poly, skip Mesh Collider first; use a Compound Collider instead to avoid frame drops. Adjust collider positions to match key areas (like edges or protrusions) for a better fit.