Blender Cloth Mass and Tension Stiffness Explained

In Blender's cloth simulation system, achieving realistic fabric behavior relies heavily on fine-tuning physical properties. This guide explains the exact roles of two fundamental parameters: Mass and Tension Stiffness. Understanding how these settings govern the weight, momentum, and elasticity of your 3D mesh allows you to accurately simulate everything from light, floating silk to heavy, rigid canvas or stretchy spandex.

What Does Cloth Mass Control?

Cloth Mass determines the weight of the fabric, calculated per vertex (or total object mass depending on the workflow). It defines how the cloth responds to external forces such as gravity, wind, collisions, and inertia.

  • Inertia and Gravity Response: Higher mass gives the cloth more physical momentum. Heavy cloth pulls downward strongly under gravity, falls faster through resistance, and takes more force to change direction when moving. Low-mass cloth feels floaty, reacts instantly to small air currents, and settles gently.
  • Force Field Interaction: Wind and turbulence fields push low-mass cloth easily, making it ideal for flags, banners, or lightweight curtains. High-mass cloth resists wind forces and requires significantly higher force strengths to move.
  • Practical Examples:
    • Low Mass (0.05 – 0.15 kg): Silk, satin, thin paper, lightweight sheer curtains.
    • Medium Mass (0.3 – 0.5 kg): Cotton t-shirts, light blankets, standard clothing.
    • High Mass (1.0 – 3.0+ kg): Heavy leather, denim, canvas, thick burlap sacks, heavy rugs.

What Does Tension Stiffness Control?

Tension Stiffness controls the cloth’s resistance to being stretched along the edges of its mesh. It dictates how much the fabric can elongate when pulled by gravity, motion, or collisions.

  • Stretch Resistance: When tension stiffness is high, the distance between vertices remains rigid, preventing the cloth from deforming like rubber. When tension stiffness is low, the mesh stretches easily under load.
  • Draping and Wrinkle Formation: High tension stiffness creates broad, sharp folds and maintains the cloth's original dimensions. Low tension stiffness produces softer, sagging folds and allows the fabric to hang noticeably lower under its own weight.
  • Practical Examples:
    • Low Tension Stiffness (1.0 – 5.0): Spandex, rubberized sheets, knitted wool, elastic sportswear.
    • Medium Tension Stiffness (15.0 – 35.0): Standard cotton, polyester blends.
    • High Tension Stiffness (50.0 – 100.0+): Stiff denim, sails, thick canvas, non-elastic leather.

How Mass and Tension Stiffness Work Together

Mass and tension stiffness are directly codependent. If you increase the cloth mass without increasing the tension stiffness, the fabric's heavier weight will naturally stretch the mesh downward, causing unnatural rubbery sagging.

To achieve realistic results:

  • Heavy, Non-Stretchy Fabrics (e.g., Denim): Pair high mass with high tension stiffness.
  • Light, Non-Stretchy Fabrics (e.g., Silk): Pair low mass with high tension stiffness.
  • Heavy, Elastic Fabrics (e.g., Thick Knits): Pair medium-to-high mass with low-to-medium tension stiffness.

If high-mass cloth continues to stretch unrealistically even with high tension values, increase the Simulation Quality Steps in the Cloth settings to give Blender more calculation passes per frame to enforce structural stiffness.