The collision shape for the upper chest to the shoulders should be embedded into the neck.
✘ Wrong: The collision shape sticks, producing a gap between the back and the hair.
✔ Right: When placed closer to the neck, allows the hair to fall properly to the back.
When setting the size of the collision shape, factor in the widest width of the limbs, especially for the thighs.
✔ Right: Set the thickness of the collider to the largest diameter of the thigh.
If the collider is smaller than the largest diameter of the thigh, then cloth worn over the legs will sink into the mesh, like the figure to the right.
The colliders for the trunk of the body must be connected, without any gaps in between.
✔ Right: Colliders for the trunk of the body must be big enough to connect with each-other.
✘ Wrong: Leaving a gap between the colliders inside the body can create gaps where collision with the surround clothe can fail.
Make sure the colliders for the buttocks are properly sized to cover the region.
It's recommended to use the capsule collider instead of the sphere shape to support the shape of the breasts.
✔ Right: Using the capsule colliders for the breasts prevents the hairs from falling into the chest.
✘ Wrong: Using the sphere colliders for the breasts makes it easy for the hairs to intersect with the chest.
Situations where certain clothes forms a wide gap from the body due to the collision shapes can be fixed with a simple setting:
✔ Right: Use the cloth's wide buffer gap with the PhysX Soft vs Rigid Collision setting. Also, consider changing the collision shape.
The collision shape settings here has no effect on the cloth itself.
Certain cloth may cut right into the colliders because the physics weight map might have grey-scale data or gradients. Consider editing the weight map to fix this issue.
Grey-scale data in the weight map can cause the clothe to sink into the colliders.
A completely white weight map will rely 100% on the physics engine to conform around the colliders.
For high fidelity simulation of the cloth physics, make sure to use the By Frame setting in the timeline:
Don't put too much detailing into the weight map for the clothe. The complete dark areas must also cover the included vertices completely. You can visualize the weight map coverage by saving it out as a diffuse map for the clothe (with wire-framing and shaded mode on).