What makes the vintage bubbles yellow?

[misterbigbo]

Hi folks, I am relatively new to vintage MOTU collecting, and am curious if there are specific factors that cause MOC MOTU bubbles to yellow.

I have had a few 25-30 year old MOC toys from several lines, and have only had a couple yellow bubbles. A ROTJ Obi Wan and a Rambo are the best (worst?) examples I can think of. In both cases the bubbles were yellow and cracked, as if the plastic had weakened considerably, and when handled seemed to weaken further. My other toys from Kenner and Mattel and other brands have held up well, but when I look for vintage MOC online I seem to see yellow bubbles on MOTU more often than other makers'.

So is it sunlight, moisture, temperature, or a combination of the above? Are MOTU more susceptible than other toy lines for some reason, or am I imagining this? Thanks!

[Stargeezer]

So is it sunlight, moisture, temperature, or a combination of the above?

I would say all of the above + kind of plastic used for the bubble.

For example i you look at the star wars
Vintage line, most Rotj and Potf figures will have yellowed bubbles, Whilst SW cards mostly Will have clear bubbles. Also tri logos have clear bubbles most off the time, but these are more prone to denting, because of thinner plastic i believe.

I think you can compare MOTU with Rotj and Potf bubbles and these are just more prone to yellowing.

[Dr_SLUMP]

Light, especially sunlight plus oxygen. Oxygen causes dark discoloration while light that contains UV does the yellowing.