reactor provides two different types of soft body: mesh-based soft bodies, where the underlying mesh is directly deformed, and Freeform Deformation (FFD) bodies. With an FFD body, reactor encases the original shape in a simpler FFD lattice. Then the simulation uses the lattice, rather than the object itself, as the soft body's shape. As the lattice deforms, it updates the original shape so that it, too, appears to deform.
FFD soft body deformation applied to a character’s nose
FFD bodies are less accurately modeled than mesh-based soft bodies, but also less computationally expensive to simulate. Because of this, it's generally advisable to use an FFD-based soft body when deforming a complex mesh. As a general rule of thumb, if a mesh has more than 200 triangles, it's probably a good idea to use an FFD-based soft body.
Different FFD dimensions produce different behavior. When using FFD(box), set the dimensions to a number that leaves the FFD vertices evenly distributed over the lattice. You can also use the Conform To Shape command to make the FFD lattice better represent the underlying geometry.
When on, reactor animates both the FFD lattice and the transformation of the object. In some situations, the deformation calculated by the FFD modifier is more consistent if the object transformation follows the FFD lattice.
Not animating the object transform can cause the FFD modifier to apply strange deformations.
Animating the object transform (turning on Animate Transform) fixes the problem.