My grandson was playing with one of my older yo-yos, a YoYoJam Heavy Gravity from the 2005 World YoYo Contest. He threw it down and it hit the hardwood floor, shattering dramatically. Interestingly, when I picked up one of the larger chunks, I could break off pieces with my bare hands easily. I guess this particular variety of polycarbonate doesn’t age well. 
I believe something similar happened back in 2015 when I shipped off a Henry’s Python to an Ebay buyer. He sent back pictures of the yo-yo in pieces, even though I’m sure it was packaged very well. I was wondering if there is a particular lifespan for polycarbonate material. I mean, I have plastic yo-yos from the 1950s that aren’t (as yet) crumbling, but I generally don’t play them and haven’t tried to break off pieces with my bare hands. 
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Yoyojams are known to crack so im not suprised
I have an entire Old school Yomega soft case FILLED with Heavy Gravity yo-yos…… from my Yoyojam years.
Almost every one of them is cracked to one degree or another.
I prolly have more cracked Yoyojam yo-yos than most people on this forum would ever see in their life, lol.
I have not tried to squeeze them into pieces. They just crack around the center.
……I have Brand new Freehands in the packages from way back when the Freehands were released. I seriously doubt they are cracked….at all. But do not yet feel compelled with curiosity to open them to find out?
In have some new in packages ‘Renegades’ from years ago. I need to check them out just because it’s easier to open them without a box cutter, lol.
I do remember back in the late 90’s and early 2000’s, I use to go the toy Fairs out here in Cali. Usually ended up getting a few of the clear plastic brain yo-yos. Several of them have literally disintegrated in the cabinet I stored them in. Almost like they were made out of sugar.
I’m sure glad I never planned on a lot of my older yo-yos having any future resale value, haha.
Certainly would have been a very poor investment.
In the next day or two, I will post some mass fatality pics of sad yo-yos.
I have had original freehand explode on the shelf. I think they were from right at the end of that tools lifespan. It’s funny to see what ages and doesn’t. 07 888s all need new orings by now.
The oldest grandson ended up taking home a beautiful speckle-anodized YYF 44, and the younger one took home a Stunt Pilot. Hope the Stunt Pilot doesn’t explode. 
Proyonium has a 1million year half life 
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I believe all the plastic yoyos mentioned here are injection molded.
From what I’ve read, the heating required for the injection molding process can reduce the molecular weight of polycarbonate. This can significantly decrease the ‘lifespan’ of the plastic.
Yoyos turned from rods, however, should not suffer the same degredation.