Napped cloth has fibres leaning microscopically in one direction. On a snooker table that nap changes roll speed and distance, so the cloth must be laid consistently.
Finding the nap
Run a palm or soft brush over clean cloth: one direction feels smoother and the other slightly rougher. With a new cut, follow the maker's markings and instructions rather than the way the roll happened to sit.
Effect on play
A ball travelling against the nap loses more energy. The difference appears on long pots and positional shots. Keep the direction consistent on the bed and, where required by the cloth design, on the rails.
Recovering correctly
Before removing old cloth, the technician should photograph its orientation and mark the table's baulk end. After stretching, check for wrinkles, clean joins and ball roll in both directions.
Brushing harder or more often does not remove a speed difference; it only accelerates fibre wear.