Jean-Francois Fortin: Setting Skin with syCloth

Jean-Francois Fortin is a TD Chraracter Rigger currently working in a feature film production. Jean-Francois was kind enough to share with us here his experience using syCloth to create skin over his digital muscles:

"I had been doing 3D professionaly since 1999, using Sofimage at first, before switching to Maya. Two years ago I discovered syFlex, which is the best cloth simulation I have tried. It's really fast and easy to use! With a couple of hours on syFlex you can get pretty nice results."

"SyFlex is great for the kind of work I do, as I need to reach realistic results in a short amount of time, and everyone knows how important time is in 3D production... Now with syFlex 3.0, come the implementation of new features like sySkin and syFlesh, and the rescale attribute, which l love. The blend cache is also really useful for action shots, where you have to get different settings depending on the movement.

For this tutorial, I used syCloth and the rescale attribute because it enables me to have the skin shrink on the muscle whatever happens. l hope you will enjoy my tutorial."

Jean-Francois used syFlex 3.0 on Maya 6.0.

01. CREATE THE MUSCLES to be skinned:


Jean-Francois' muscles model

Here is my model with all the muscles I am going to skin piece by piece.

I select all my muscles and bones and use Maya's skin on selected bones. Here are the values I use:
Max influences: 1
Dropoff Rate: 4

I use those settings because I want each muscle (OBJECT) to be skinned only at the closest joint, so that I don't have vertices skinned to some bones far from the main bone-set. This helps me work faster.


After all my muscles are skinned properly, I am using Sculpt Deformer and Blend Shapes to add some muscle deformations. Here is an example of shapes with Sculpt Deformer on the arm.

I added some Sculpt Deformer on the stomach area and on the pectoral area as well. You can add some jiggling to some part of your system to achieve more realism, either with Maya's internal Jiggle, or with dynamic curve and a combination of wrap. There is also syFlesh now which can be used for that purpose. But those things are for another tutorial...

03. CREATE YOUR SKIN SHAPE, make a poly mesh:


Modeling the skin shape

Here is the skin mesh I built in Maya, to be turned into a syCloth. You should try to keep the topology really clean, the simulation responds to every muscle line so keeping it simple will give you the best results.

I skined every piece separately using Maya's smooth skin, sculpt deformer and blend shape to fix some areas and achieve some sort of fake muscle deformation.

04. CREATE CLOTH, turn your mesh into skin:

When you are happy with your mesh, you are ready to setup the skin with syFlex.
I am using a low-res mesh for my simulation, so the computation is really fast, and I can make many tests. Later I am using Wrap Deformer to deform a high-res mesh.

Select your skin mesh and call:   Syflex > Cloth > Create Cloth

I am using syCloth and not sySkin because of one attribute which doesn't exist for sySkin yet, the Rescale attribute. You will see why later.

05. CREATE WEIGHT, add Volume and Global Damping:


Entering the values for the forces in the syEdit window

Now that your mesh is converted into a syCloth, you can add forces onto it. Select it and call:

Syflex > Forces > Create Volume

The Volume force preserves the volume of the shape, this force works better on a closed mesh, but it is very useful here.

Add damping:
Syflex > Forces > Create Damp

The Damp force slows down the animation and at the same time removes any unwanted jiggling which is created as a result of quick movement. The more violent the movement in your animation, the higher you should set the global Damping (the Damp force value). However, raising this value also increases the computation time, so be careful with it.

06. CONNECT THE SKIN, pin it to the bones:


Skin pinned to the wrist

Select the extreme vertices of the skin, and the object it needs to be connected to, like the wrist muscle in the example here. Pin the skin to the muscle, by selecting both and calling:

Syflex > Constraints > Pin

I pined the skin in the example here to the neck, the wrist and the base of the torso.



Collisions and Friction

Now you can start adding collisions between the skin and the muscles or bones it needs to be affected by. Remember to name all your collisions, it helps to keep track of which object is a colider and which is not. In this scene I have more than 45 collision objects so naming them was really useful!

For the collisions I entered the following values in the attributes:

Envelope_ext: 0.03
Envelope_int: 0.03

08. DEFINE SKIN BEHAVIOUR, by using the Friction attribute:

For some area we want the skin to stick more to the collision objects, and in other areas, it needs to have a sliding effect. Here is an overview of the different Friction values I entered for the different skin parts:


Friction values

09. HAVE YOUR SKIN SHRINK AROUND THE MUSCLES, by using the Rescale attribute:


The syCloth Attributes

In the syCloth Attributes Editor window, you will find a new attribute introduced in syFlex 3.0; Rescale. Rescale is extremely powerful for our skin simulation. It makes the skin shrink around the muscles!

When you have a muscle bulge or any deformation, you can see clearly the sliding of the mesh on that muscle according to the Rescale value. For my simulation, I found that the value 0.85 works best.

I worked with the Damping to help remove some wavy effects which occurred.

As to the rest of the attributes: Mass Density will influance the animation although we are not using Gravity here, so pay attention to it. I left Self Envelope on 0 because there is no self collision here.


After you have the setup in place; Skin, Forces, Collisions and Friction, you can start tweaking the parameters, until you reach the effect you are after. While testing, you can drop the precision attribute to 0.01. The simulation will be less accurate, but much faster.

For better understanding of how the body and the skin move, just look in the mirror! I also looked at many anatomy books.

I hope you liked this tutorial. If you have any question or comments, please send me a email at

Jean-francois Fortin is a TD Setup Artist. You can visit his website here:

In-depth information about every aspect of SyFlex, including the elements used in this tutorial, are available in the software documentation. If you have any additional questions, do contact us at:


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