“Fast cloth” is not a single universal specification. Ball speed is shaped by the fibre blend, nap direction, tension, dust and the condition of the balls.
Fibre and nap
Wool-rich and synthetic blends create different friction. On napped cloth, direction matters: a ball can travel faster with the nap and slower against it.
Tension and recovering
Sags, wrinkles and incorrect panel orientation produce local speed changes. Have recovering done by a technician who understands the slate and rail construction.
Cleanliness
Chalk and dust increase friction. Brush the surface gently in the nap direction and use only stain products approved for that cloth.
Compare speed under similar room temperature, clean balls and a correctly levelled table; otherwise the test says little about the fabric itself.