I always assumed the plastics are the main concern since UV light and heat can cause plastics to become brittle over time.

The styrofoam that helps absorb impacts degrades over time. But also they don’t want to guarantee the seat will be safe indefinitely, otherwise they’d get sued when a kid gets hurt in a 20 year old seat.

>all synthetic materials that don’t seem to decay as quickly as the manufacturers suggest

They actually do! The plastic will degrade over time, from both UV light from the sun, as well as extreme heat or cold.

Now, that said this is really just a reduction in the effectiveness of the car seat, which for a lot of other applications isn’t really a big deal. But considering the entire point of a car seat is to *protect a child* it’s definitely important that people are informed that a given car seat is going to do a worse job at that.

Are companies incentivized to tell you to buy more of their product? Of course. Do they want to not get sued when their 30-year-old car seat gets a child hurt? Of course. But there is definitely a lot of truth in those expiration dates.

The materials deteriorate, stuff is designed for only certain number of jerks, tightening, loosening. Over a period of time it might reach a stage of catastrophic failure

Regulations are written in blood

Also
https://letmegooglethat.com/?q=why+car+seats+expire+

I hate how people have started using Reddit for very trivial search.

Internet is a library, spend some effort going thru it instead of asking people to spoon-feed best answers

Nothing expires. Structural plastics maintain their strength and do not embrittle under heat or UV to the point where it would compromise their effectiveness as a car seat. It’s a total scam.

context: I’m a mechanical engineer who has working in reliability and structural durability in the automotive industry. I get angry when people insist that you can’t pass down a car seat, but insist on making a poor parent go out and buy new while throwing a perfectly good one in the garbage.

NY Times asked Graco why their car seats have expiration date 6 years after manufacturing when it’s not required by law. Graco rep stated plastic does not have any problems until 10 years at a minimum.

The real reason for the expiration date is that regulations change over time and Graco doesn’t want people using seats with old, less safe designs.

This is my guess: I would also assume car seat manufacturers don’t want to service recalls for really old seats as it gets expensive. Saying the seat has expired makes more people get rid of their old seats.

To answer some of your other questions that other people haven’t yet, you can tell it’s expired by checking the expiry date. Typically there in two places on the car seat, plus in the owner’s manual. While the seat certainly won’t explode the day after its expired, the materials that provide protection in a crash can become less efficacious over time. Given that a properly installed seat can save a child from a completely mangled car… It is a worthwhile thing to not play fast and loose with. That said, because of how regulated the car seat industry is, there isn’t a different in efficacy based on price. A 100 dollar carseat will protect a child just as well as a 500 dollar carseat. Lastly, most car seats now last for about ten years, so my guess would be that the oldest ones on the shelves go to clearance for all too happy parents to save some money while only losing a year of life for the carseat.

Source: I’m a CPST

Corporate responsibility.

If some kid gets hurt in a seat that’s past the artificial “expiration” date they walk away from it. Regulation-change doesn’t affect this (it’s grandfathered from date of manufacture) and styrofoam changes so slowly that it’s considered a “forever” plastic. Bike helmet makers try this stuff with the same material but the NIH has called them out on it.

Resource: [Age Does Not Affect the Material Properties of Expanded Polystyrene Liners in Field-Used Bicycle Helmets](https://pubmed.ncbi.nlm.nih.gov/26902784/)

I’m not saying that this is the main reason but adding it since I didn’t see it. Ozone is found in the atmosphere in small concentrations everywhere. Ozone undeniably degrades plastic. Over time, this will cause plastic to lose strength and structure. So even if left in the dark, the car seat will go through some aging, albeit much slower than the expiration date comes.

Have you ever had a plastic lawn chair that one day the leg just snaps off?