According to Appendix 7 in the "The Rules of Sqaush", The World Squash Federation (WSF) specifies that Yellow Dot balls must be tested for "rebound resilience" at 45c.
The following specification is the standard for a yellow dot ball to be used under the Rules of Squash.
According to the article "Balls on Test" on http://www.squashplayer.co.uk, Dunlop performs this test to ensure conformance with that rule.
Rebound resilience is simply a measurement of the height a ball bounces off a hard surface. The same balls are conditioned first to 23oC and then to 45oC and dropped from a height of 100 inches
According to the article "Ball Behaviour", also located on http://www.squashplayer.co.uk, 45c is a common surface temperature at which the Yellow Dot is used.
Obviously, the ball does not continue indefinitely to heat up; eventually equilibrium is reached where heat loss to strings, wall, floor, and air is equal to heat gained from deformation. This point is normally at around 45oC, which is why the WSF’s rebound resilience specification is calculated at that temperature.
Since 45c is a standard surface temperature used by Dunlop and the WSF for the Yellow Dot, I use that surface temperature as a benchmark when making some comparisons of surface temperatures. 45c is 113f. Since this study was done using Fahrenheit, I use the 113f figure.