Why are hockey pucks so indestructible? After watching a hockey puck be exposed to extreme heat as well as extreme cold, the puck seems to end up in pretty good shape.  I can sort of understand the puck vs. hot ball of nickel since the area of contact is relatively small (and I've always been told that heat rises).  The other one, I'm confused why it fared so well.
In my experience, objects that are exposed to liquid nitrogen long enough become very brittle.  This leads to those object shattering upon impact if not spontaneously.  So what makes the hockey puck special to avoid such a shattering?
 A: 
In my experience, objects that are exposed to liquid nitrogen long enough become very brittle. This leads to those object shattering upon impact if not spontaneously. So what makes the hockey puck special to avoid such a shattering?

Liquid nitrogen's boiling point is $-196\:\mathrm{Celsius}$ which is below the glass transition temperature ($T_g$) of most rubbers. Below that temperature an elastomer (rubber) becomes fragile like glass.
A puck is never exposed to that kind of temperature. The lowest will be in the order of about $-10\:\mathrm{Celsius}$ to $-20\:\mathrm{Celsius}$, which is well above the $T_g$ of most rubbers.
Pucks can take a lot mechanical battering and abrasion because they're made of specially formulated, sulphur vulcanised rubber, mostly based on high molecular weight natural rubber I believe. Optimal formulations can be obtained by statistically controlled designed experiments.
An important ingredient in black, reinforced vulcanised rubber is HAF (High Abrasion Furnace) carbon black, which as the name implies imparts high mechanical strength to the rubber vulcanisate.
Vulcanised rubber also resists high temperatures quite well because the three dimensional network of cross-links that connect the polymer chains means the material simply cannot melt (but it can of course degrade chemically at high temperatures).
A: Because the material that pucks are made out of are 'vulcanized'.
This means that is it chemically changed to with sulphur to make it more durable.
