Blender Cloth Simulation Internal Springs Explained

Blender's cloth simulation includes an Internal Springs feature designed to give three-dimensional volume, internal structure, and soft-body-like elasticity to enclosed meshes. This article explains what the internal springs setting is, how it operates within the cloth modifier, its main benefits over soft-body physics, and how to configure its key parameters for realistic volumetric simulations.

What Are Internal Springs?

By default, Blender’s cloth physics engine only calculates forces along the surface edges and faces of a mesh. This standard behavior makes any model act like a hollow shell of fabric. When applied to a closed, three-dimensional object—such as a cushion or a rubber ball—the model collapses in on itself when impacted because there is nothing supporting it from within.

The Internal Springs setting solves this by generating invisible spring connections across the interior space between opposite vertices. These virtual internal connections exert tension and compression forces, allowing a 3D mesh to maintain its structural volume and resist collapsing without requiring an external force like pressure.

Cloth Internal Springs vs. Soft Body Physics

While Blender provides a dedicated Soft Body modifier for volumetric deformation, using the Cloth modifier with Internal Springs is often preferred for several reasons:

• Performance: Cloth simulations calculate faster and handle complex geometry more efficiently than the soft-body solver.
• Surface Detail: It preserves realistic fabric wrinkling, creasing, and folding on the outer surface while retaining the bulk shape underneath.
• Collision Stability: Cloth collisions are generally more stable and easier to configure against complex collision geometry.

Key Settings and Parameters

To use internal springs, navigate to the Physics Properties panel, enable Cloth, and check the Internal Springs subpanel. The following settings determine how the springs generate and behave:

• Max Spring Creation Length: Defines the maximum distance between two interior vertices across which a spring can form. Setting this properly prevents springs from crossing large open gaps in complex or concave shapes.
• Max Creation Angle: Limits spring generation based on the angle between the vertex normal and the connecting spring line. This prevents unnatural internal connections across sharp outer corners and seams.
• Tension Stiffness: Controls how strongly the internal springs resist being stretched apart. Higher values make the object firmer when pulled.
• Compression Stiffness: Controls how strongly the internal springs resist being compressed. Higher values make the object firmer and harder to squish, while lower values create a softer, foam-like response.
• Vertex Group: Allows the user to assign a vertex group to restrict or weight where internal springs are generated, useful for objects that need varying stiffness throughout their volume.

Common Use Cases

Internal springs are ideal for simulating:

• Cushions, pillows, and mattress padding.
• Upholstered furniture and plush stuffed toys.
• Biological tissue, fat, and muscle deformation.
• Dense materials like foam, sponges, and rubber blocks.