1. n. 
A subjective description of a filter cake, especially its toughness, slickness and hardness. A mud engineer makes these observations, which are recorded on the mud report along with filtrate volume and cake thickness. With increasing experience, the engineer's observations can become less subjective.
See: acrylamido-methyl-propane sulfonate polymer, differential sticking, dynamic filter press, dynamic filtration, filtercake, filter press, filter-cake thickness, low-pressure, low-temperature filtration test, mud engineer, static filtration