Every single styrofoam cup I have ever seen, from store bought to the ones in fast food take out places, always have a thicker ring of styrofoam on the top 1/8" to 1/4". Why is this? What purpose does the extra thickness serve on the top lip of the cup?
It’s so you won’t squeeze it and spill all the contents when you pick it up.
…and also for extra insulation against hot liquids.
Added ring strength at the rim, so that it retains its cup shape and you don’t spill hot coffee on your crotch.
It’s probably a fraction of a cent cheaper than just increasing the wall thickness overall.
A negligible contribution, at best. If the liquid is that high in the cup, it is either spilling or being drunk. I vote for the structural strength analysis.
It may also help in the stacking. The rim may serve as a “stop”, preventing cups from fitting too close and sticking together.
There might be something in this. The cups we have at work are of uniform thickness throughout – see, they’re not all like that – and they stack very tightly and so can be difficult to separate.
Silly me!! I thought it was for the lid… something to snap over.
If they were that thick all over, they’d stack much higher, and the larger packages would be harder to transport and store.
It’s probably a combination of “all of the above.” Also, the “stop” factor aids in not spilling when the cup slips down through your fingers - they’ll catch the rim. It’s easier to pick up a hot styrofoam cup just beneath the bulgy part for this reason.
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- I say “none of the above”: that it has to do with helping it seal better in your mouth. Note that even paper cups will have a rolled top-edge. Now take a paper cup, use a razor blade to slice the top edge off, and then try to drink out of it. The sharp edge doesn’t seal in the corners of your mouth very well unless you press it into your mouth fairly firmly, and that is quite uncomfortable to do.
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- I say “none of the above”: that it has to do with helping it seal better in your mouth. Note that even paper cups will have a rolled top-edge. Now take a paper cup, use a razor blade to slice the top edge off, and then try to drink out of it. The sharp edge doesn’t seal in the corners of your mouth very well unless you press it into your mouth fairly firmly, and that is quite uncomfortable to do.
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Yes… but the “thin” part of most styrofoam cups is at least as thick as the rolled-over part of a paper cup, so I don’t see that this follows.
There are foam cups that are uniform all the way up. I seem to be visualizig some standard-blue pattern for some reason. I usually think of these as jumbo-sized cups, like maybe at a stadium to justify $6 per 32 ounces of soda. They also seem “cheap” to me in that they’re not as visually appealing (who’d’ve thunk aesthetics would matter to me on this?).
Since the Straight Dope is here to fight ignorance . . .
Dow Chemical: There isn’t a coffee cup, cooler or packaging material in the world made from STYROFOAM.
Yeah, and Adobe says you can’t call it “photoshopping” when you edit a picture. Corporations seem to get a kick out of waging losing trademark battles with the general public.
[and now back to your regularly scheduled, non-hijacked thread]
From that cite, I understand “Styrofoam” is a brand name and all, but “The color Blue is a Trademark of The Dow Chemical Company” seems like it’s going too far. 
So can I be sued for typing this post in blue?
[sub]This post has been Blued by the… oh screw it.[/sub]
From that page’s text, it seems like there may be more difference between “styrofoam” and “expanded polystyrene beads” than the trade name. Maybe styrofoam is produced in a different way and ends up being one large blob of polystyrene, rather than a bunch of fused beads, for example.
The thing about ‘the color Blue’ refers only to expanded polystyrene foam products; you can type in blue, but you can’t make insulation out of expanded polystyrene foam that’s blue in color.
I think it’s for structural strength (the cups would be easy to distort out of shape without a band of thicker material at the top), to aid stacking (holding the cups apart so they don’t stick), and also to make it easier to attach a lid. The band at the top of an EPS cup is about the same width as the rolled rims on paper cups, so lids for paper cups also fit EPS cups. It would probably still be possible to attach a lid without the rim, but it’d have to be designed for a different thickness.