The Constrain Strand Length compound makes the strands follow particles like trails. If the particles leave the emitter, the strands follow behind like strings that always keep the same length. This compound is also useful for creating hair, if you're creating with particle strands that have no emission Speed. The strands don't follow the particle's path exactly as they do with Align Strand with Particle Trajectory compound.
Create strands with the Create Strands or Generate Strand Trails compound, then plug this compound's Execute output into a PostSimExecute port on the Simulation Root node or in a port on the ICETree node.
For information, see Keeping Strands the Same Length [ICE Particle Simulations].
