Many pickleball enthusiasts are willing to brave extreme cold or hot temperatures to play their favorite sport. While we all know (intuitively) that warmer temperatures translate into softer balls, has anyone determined quantitatively the relationship between ambient temperature and ball stiffness? Further, how does the ambient temperature affect ball bounce and velocity? In this article we test eight popular pickleballs to determine how their stiffness properties change with temperature and explain how this affects ball performance. First, we need to look at molecular science.
Molecular Science
The plastic that makes up a typical pickleball consists of long chains of molecules (polymers) that are intertwined and linked together. Some of these interconnections, or cross-links can be very strong (such as covalent or ionic bonds), which provide the plastic with rigidity and enable it to be formed into shapes like pickleballs. Other interconnections are weak (such as Van der Waals forces) which cause the plastic to become brittle (stiff) or ductile (soft) when the temperature changes.
The Van der Waals forces are essentially electrical forces of attraction between the electrons that make up the atoms of the polymer. These forces are inversely proportional to the distance between atoms. That is, when the atoms are closer together the forces are stronger, and vice versa. At elevated temperatures, the electrons become very active, creating greater distance and lower forces of attraction among the atoms. This causes the plastic to become very ductile or soft. At reduced temperatures, the electrons slow down and the atomic distance decreases, thereby increasing the intermolecular forces and making the plastic brittle or stiff.
The differences in stiffness of the pickleball is of interest to players because the ball behaves differently at different temperatures. As the temperature decreases, the ball becomes very stiff and faster and may be prone to cracking. As the temperature increases, the ball becomes spongy and slow. How sensitive are the different pickleballs to temperature changes? Are some pickleballs better for colder or warmer climates?
Pickleball Stiffness Tests
The most accurate way to determine a pickleball’s temperature sensitivity is by use of a sophisticated instrument known as a dynamic mechanical analyzer, or DMA. Although we have access to such an instrument, we simplified our testing by using our force-displacement gauge and measured the stiffness of eight popular pickleballs at different temperatures (Figure 1). We first placed the balls in a freezer set to +30 deg F (-1 deg C) for a minimum of 15 minutes. We next tested the balls when they reached room temperature (+73 deg F / +23 deg C). Finally, we tested the balls after placing them into a warming oven at +120 deg F (+49 deg C) for 15 minutes.
Test results at the three temperatures for all eight balls are shown in Figures 2a-c. Although the results are approximately linear, a trendline was fit through each curve with the intercepts set to zero. This yields the slopes of each line which are equal to the stiffness of each ball at each temperature.
As an illustration, we show the force-displacement relationship of the Franklin X-40 ball at the low, room, and high temperatures (Figure 3). This data shows that the slopes of the force-displacement curves become shallower with increasing temperature indicating a softening of the plastic. Further, we can see that the ball stiffness at the high temperature is roughly one-half of its stiffness at room temperature, and roughly one-third of its stiffness at the cold temperature!
Further interpretation of these charts suggests that the spread in the data appears to be greater at higher temperatures than at lower temperatures (Table 1). That is, at colder temperatures the data appears to more tightly clustered with similar slopes. As the temperature increases, the data appears to be more widely dispersed with greater differences among the slopes. This might indicate that the balls will perform similarly at lower temperatures and differences in performance will be more apparent at higher temperatures.
Conclusions and Recommendations
Our data suggests that certain balls* are better suited for playing at cold and hot temperature extremes due to the following:
- In cold climates, the plastic becomes very stiff and brittle, which limits its ability to deform and absorb the energy of impact with the paddle. Some “springiness” of the ball is desired, as the potential energy stored in the ball during impact is released in the form of kinetic energy that increases the velocity of the ball on return. In fact, at cold temperatures, certain balls will be too stiff, and will not bounce very well and may be prone to cracking. If you play in cold climates, you should select a ball with a low temperature stiffness that is less than 180 lb/in, such as the Centaur Republic or Core Outdoor. These will provide good bounce with a reduced risk of cracking.
- In warm climates, the plastic becomes very soft and ductile, and will deform considerably when struck by the paddle. In a perfect world, the large deformation would be desirable since the energy stored to compress the ball would translate into increased velocity on release. However, on a molecular scale, the increased deformation results in increased motion of the polymer chains, resulting in friction and higher damping that dissipates this energy. Furthermore, repeated large deformations can result in cracking of the ball. A ball that is too soft at warm temperatures will therefore seem slow or sluggish. If you play in warm climates, you may want to select a ball that is stiffer with a high temperature stiffness that is greater than 80 lb/in, such as the Vulcan Pro, Joola, or Wilson Tru 32.
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