Interior

In Blender's case, the ideal length is the original edge length which you designed as a part of your mesh,even before you enable the Soft Body system. Until you add the Soft Body physics,all springs are assumed to be perfectly stiff: no stretch and no squeeze.

You can adjust the stiffness of all those edge springs, allowing your mesh to sag, to bend,to flutter in the breeze, or to puddle up on the ground.

To create a connection between the vertices of a soft body object there have to be forcesthat hold the vertices together. These forces are effective along the edges in a mesh,the connections between the vertices. The forces act like a spring.Fig. illustrates how a 3×3 grid of vertices(a mesh plane in Blender) are connected in a soft body simulation.

Luckily, Blender allows to define additional virtual connections.On one hand you can define virtual connections between the diagonal edges of a quad face(Stiff Quads Fig. Additional forces with Stiff Quads enabled.),on the other hand you can define virtual connections between a vertex and any vertices connectedto its neighbors' Bending Stiffness. In other words, the amount of bend that is allowed betweena vertex and any other vertex that is separated by two edge connections.

The characteristics of edges are set with the Springs and Stiff Quads properties in the Soft Body Edges panel.See the for details.

Tips: Preventing Collapse

To show the effect of the different edge settings we will use two cubes(blue: only quads, red: only tris) and let them fall without any goal onto a plane(how to set up collision is shown on the page Collisions).See the .

In Fig. With Stiff Quads., Stiff Quads is activated (for both cubes).Both cubes keep their shape, there is no difference for the red cube,because it has no quads anyway.

Bending Stiffness

The second method to stop an object from collapsing is to change its Bending stiffness.This includes the diagonal edges (damping also applies to these connections).

In Fig. , Bending is activated with a strength setting of 1.Now both cubes are more rigid.

Bending stiffness is the strength needed for the plane to be deformed.