The marriage between a core and coverstock is a delicate one. The coverstock must allow the core to express its dynamics in a manner that is consistent, enabling the bowler to have the confidence that they will see a ball reaction that they can predict.
The coverstock must read the midlane, enabling the coreï¿½s RG, differentials, and mass bias to determine the proper shape of the breakpoint and the amount of backend hook potential. Core/coverstock combinations are chosen by a ball testing procedure that uses league bowlers to evaluate the products. Each different core generally is evaluated with multiple coverstocks, searching for the ultimate combination.
Polyester coverstocks are a non-porous, slicker surface and are designed to minimize friction. Polyester coverstocks are best when trying to throw the ball straight. Standard urethane coverstocks provide more friction than polyester but do not have the backend hook potential as reactive resin and particle resin coverstocks.
It is a non-porous surface which will not absorb lane oil. Reactive coverstocks are a urethane base with an additive that creates an internal pore structure to absorb lane oil and increase surface tackiness.
In general, they retain more energy through oil and release energy stronger in the backend friction. The transition from skid to hook is more angular than standard urethane and particle resin coverstocks, creating more of a skid/snap ball reaction. Particle resin coverstocks have silica particles mixed within the reactive resin.
Particles provide more traction in the oil than reactive balls and will have a smoother backend hook. They are more controllable in the backend friction with a more mild change in direction.