Subject: Why does a rubber ball bounce higher when only partially frozen/very cold?

For my science fair project, I am conducting an experiment on the effect 
of ball temperature on the height of the bounce.  I understand the effect 
on elasticity from temperature extremes (frozen vs boiling).  I am using a 
clear rubber ball.  When the ball is frozen for a day or more, it becomes 
opaque and bounces much lower than at room temperature.  But when the ball 
has only been in the freezer for a few hours (it is still transluscent), 
it bounces much higher than at room temperature.  I am dropping the ball 
from the same height onto the same surface with the same force each time.

Re: Why does a rubber ball bounce higher when only partially frozen/very cold?