As a non-robotics simulation understander, how are the specifics of the gripper/object interaction modeled? For instance, can the gripper / object materials be

As a non-robotics simulation understander, how are the specifics of the gripper/object interaction modeled? For instance, can the gripper / object materials be soft / floppy / goopy, or does the simulation assume they are perfectly rigid bodies? What kind of surface parameters does the model use? Coeff of friction, durometer of rubber surfaces touching the object, surface texture / roughness (RMS, Ra)? More?