The dry towel rule, Rule 18, went into effect August 1, 2019. The rule states:
While bowling in USBC Competition, a bowling ball cannot:
1. Have the surface altered by an abrasive.
2. Be cleaned with any liquid substance or cleaning agent.
3. Have any foreign material on it including, but not limited to:
-Powder
-Rosin
-Marker
-Paint
All bowling balls so altered or cleaned must be removed from the competition.
NOTE: Should a foreign substance appear on the outer surface of a bowling ball which cannot be removed with a dry towel, an approved cleaner may be used with the consent from a league or tournament officer