A 2005-2008 USBC Ball Motion Study found that the ball design factors that most contributed to ball motion were the microscopic "spikes" and pores on the ball's surface (considered part of chemical frictional characteristics), the respective coefficients of friction between ball and lane in the oiled and dry parts of the lane, and the ball's oil absorption rate, followed in dominance by certain characteristics of the ball's core (mainly radius of gyration, and total differential). Freeman and Hatfield (2018) explain that in most circumstances it is chemical friction—controlled by the manufacturer's proprietary coverstock formulation governing its "stickiness"—that primarily determines ball motion. Further, surface finish—modifiable by sandpaper, polish and the like—is also a material factor.