Yes, there is a difference. (Also "Pearl" is not a "finish". Finish would be things like polished, sanded etc. Pearl is referring to what the cover is made of.)
The 3 main coverstocks you see are Solids, Pearls and Hybrids.
Solid
A solid reactive ball has the tendancy to react the earliest out of the 3 categories of reactive coverstocks due to the greatest amount of microscopic reactive pores on the surface. Reactive solids come with all sorts of different finishes, including, polished, sanded, rubbing compound buffed.
Pearl
The difference between a solid reactive ball and a pearl reactive ball is the addition of mica to the coverstock chemical makeup. Mica's inclusion into the coverstock roughens out the microscopic pores to a certain degree, causing the reaction to the dry part of the bowling lane to be extended. Reactive pearl bowling balls are known for their ability to react very fast to friction. Mica flake also adds a little "sparkle" to the bowling ball's surface.
Hybrid
A hybrid reactive coverstock is a combination of solid reactive and pearl reactive coverstocks. Manufacturers recently have been creating these hybrid coverstock bowling balls to take advantage of the benefits of both pearl and solid coverstocks. Often these hybrid bowling balls offer the midlane reaction of a solid reactive and the backend reaction of a pearl reactive coverstock..
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