Determining Expiration Dates

[BW1426]

I'm not asking this because I ever plan on using an expired seat, rather just out of curiosity. When they label carseats with an expiration date how do they do this? I'm curious how different companies determine how long it takes for the plastic to break down. And, wouldn't one think that plastic would break down a lot faster in extreme temperature conditions?

[SusanMae]

I would imagine that they have some kind of machine that simulates temperature changes over x period of time and then they crash test them.

This is just speculation, but it sounds kinda cool.

Susan