Bowling Ball Shell Chemistry 101


Bowling Ball Shell Chemistry 101:


Basic Coverstocks & Reactive Polymerization




Written by: Nick Siefers


900 Global Senior Design Engineer


BS Chemical Engineering @ Purdue University 2003




The shell of the bowling ball is in direct contact with the lane surface and oil. Therefore, it is important that the designed coverstock have the correct chemical composition to maximize the relationship with the core and the desired ball motion.  There are 4 main types of coverstocks:


1)      Plastic


2)      Urethane


3)      Reactive Urethane


4)      Particle




Diving right in, the shells (coverstocks) of a modern bowling ball can be composed of several types of ingredients.  Plastic bowling balls begin with a polyester type resin mixing with peroxide that hardens to form a not so porous solid.  Plastic bowling balls came onto the market in the late 1950’s.  These balls have a surface that is very hard and abrasive resistant.  Typical sanding and polishing techniques do not have the same impact on these types of coverstocks. The amount of friction and hook for plastic balls is generated by their shell hardness.  Plastic balls are generally used when the lanes are extremely dry or for spare shots when a straighter ball path is desired.


            The initial chemical reaction for any type of urethane based ball is between two different liquid polymers, a polyol and an isocyanade, which create a chain like series of reactions that ultimately harden into the urethane shell. A general polymerization urethane reaction is noted below:



Resulting Urethane Elastomer


Urethane bowling balls were introduced in the early 1980’s.  They were originally designed to hook more than plastic balls.  The amount of hook on these balls could be manipulated without changing the hardness of the surface but rather the composition of the coverstock, however, they do not absorb oil well.  Urethane does have higher friction in the oil and on the back-ends compared to plastic.  Compared to reactive urethane, urethane balls have less friction, especially down lane, and therefore have much tamer and mild back end reactions.  Due to the less aggressive nature of urethane balls on the back ends of the lane, they can provide a gradual, more controllable hooking motion down lane.  However, this tamer reaction gives up the entry angle that a reactive urethane ball provides.  With less entry angle, there is less pin action and quite possible less carry.  Below is a 2µm x 2µm high powered microscopic view (Atomic Force Microscope) of a urethane shell.  The dark areas represent depressions or pores.  Notice that not many dark areas are present.








Reactive Urethane is simply a urethane coverstock with an added “reactive” ingredient and was marketed first in the early 1990’s.  The extra additive in the shell formula allows for microscopic pores to be formed as the polymer shell cures from a liquid to solid.  These pores are very important because they allow the reactive urethane shell to absorb lane oil.  The ability to absorb lane oil is crucial to ball reaction.  As the ball absorbs the lane oil as it travels down the lane and in between shots, the surface of the ball remains in a “dry” state.  A drier ball surface contacting the lane will have increased friction and more hook compared to a ball surface that is slick with oil and can not absorb it(oil stays on the surface of the ball).  Just as the oil in a car helps to lubricate the various parts, the oil on the lane acts a lubricant as well.  From a ball standpoint, if the chemical composition of the shell can help remove the lubricant then the total hook potential of the ball increases.  Reactive urethanes are known for their ability to slide in oil and hook on the drier backend of the lane.   Below is the same size Atomic Force Microscopic view of a reactive urethane shell.  Notice that compared to urethane, reactive urethane has many more dark areas that represent depressions in the scan.  These depressions are the pores that act to absorb oil.

Reactive Urethane








            Particle balls came out in the later portion of the 1990’s and are mainly reactive urethane shells with some particulate mixed into the shell.  Particles can be of various microscopic size, shape, and composition.  Some particles are hollow and once thrown or sanded, the particles can break open creating extra cavities for the lane oil to migrate to. These cavities help increase oil absorption as well as add texture to the surface of the bowling ball.  A practical example would be the treads on a snow tire.  The treads give a place for the snow to go so the tire can grip the road better.  Hollow particles act in this same manner resulting in earlier and more hook.  Other particles act to mainly change the surface texture, or roughness.  These shaper edged particles extend through the oil thickness and act to grip the lane.  This also amounts to increased hook in the front, oiled part of the lane.  In either case, the amount of friction between the particle ball and lane is changed as compared to a straight reactive urethane shell.  Earlier hook can be expected for particle balls.


           The overall ball motion of the previously discussed coverstocks is graphically represented below via C.A.T.S..  As can be seen, each advancement in coverstock technology has led to an increase in friction and hook.  There are variations with-in each of the different technologies but the overall trends between shell chemistry remain differentiated as noted within the data graphs. 




   In conclusion, many years of technological advancements in coverstock chemistry has led to the various types of performance.  The information and data presented in this article are the basic concepts in shell chemistry and provide guidelines for the various differences between the major chemistry within bowling ball coverstock design.