I have a dozen or more blisters that are getting yellow all over, and I notice that all the cars are made in china, is it just me or do other cars made somewhere else get Yellow? I don't have any that are not made in china, here some
Certain plastic compounds, and maybe certain paint compounds, give off airborne acids that can cause yellowing in fabrics and other plastics. Who knows what was used to manufacture those in China so it's possible something in the car itself is giving off fumes that are eating away at the inside of the bubble.
Yea, this has been discussed before... maybe can search for it here in the Hot Wheels section...
I have some too.... and they are the same way, and are in a box with other cars that are not yellowing... have a HW case with maybe 50 cars in it, all around the same year or time period, and maybe 2 or 3 have the yellowed blister... all stored exactly the same way
Word was back in the day China used different compounds in the plastic ( maybe to cut back on cost ) which made all the Blister Packs to turn yellow. You will not be able to stop the process in them changing colors whether they are in a controled environment or out in the open. They all changed to the ughly yellow Blisters you have. Crack them open and enjoy them. No Car from those few years will be worth much in the future, so enjoy them open.
The fact of the matter is ALL plastic yellows over time, some just do it more and faster than others. The difference is the kind of plastic it is and the formula used for making it. Acrylic yellows the slowest, Bakelite is one of the fastest. Polystyrene, which is one of the cheapest and most common of plastics (think styrofoam peanuts) and most likely the one being used for the blisters, can span the range - from 'normal' yellowing to hardly yellowing at all, depending, again, on its formulation. While the formulas used by the Chinese may have contributed to the fast yellowing, I still wonder if a close inspection wouldn't show some kind of air leak in the packages that allowed the blister to be exposed to the air from both inside and out.
If you happen to be interested in reading a little more about some the characteristics of some plastics, especially those used in the past, you might check out a few paragraphs on the subject in this publication (the discussion on the different plastics begins towards the end of the first page - just keep in mind it is very brief and was never intended to be considered a treatise on the subject):