The Short Version
A Soft Liner That Grips, a Hard Shell That Holds
H/S stands for hard/soft. A Comfort hard-soft nightguard is a single thermoformed sheet of two bonded layers, and the common misunderstanding is that the soft inner liner makes the appliance a soft guard. It does not.
The inner layer is soft and resilient, the same material class as a soft guard; it flexes over the height of contour and engages the undercuts. The outer layer is rigid and carries the occlusion. Grind a soft guard and the surface rebounds under the bur — you have handed a bruxer something to chew.
-
Retention comes from the liner: The guard holds without being squeezed onto the arch.
-
The occlusal scheme lives on the shell: The contacts you relieve at delivery stay relieved.