Right. But to a non-engineer, non-sciencey, non-bothered by details person, they’re close enough, especially given the lack of a better option. If you can’t explain the difference without going into production methods, it’s a good bet most people won’t recognize the distinction on their own.
This box spacer, these packing peanuts, these whatever they ares, all of those containers, these floral favorites, these cake models, and this mock-up airplane may all, in reality, be made from different stuff. But to the layperson, it’s all soft yet rigid lightweight meringue looking stuff made solid. The only catchy word we know for it is Styrofoam, and like a toddler who calls all four legged creatures “doggie”, we over-generalize.
Why did it happen the first time? I doubt there was a first time. It’s such a common human linguistic habit, I’m betting it happened simultaneously and frequently as new products came out without labeling their materials with catchy names on the front of the package in 2 inch letters. Label something
Expanded Polystyrene
FOAM FLORAL FORMS
Assorted Sizes
and it’s easy to see why people just call them styrofoam. I mean, half the word is there, right, the “foam” part. And “foam” is either transitory bubbles or it’s styrofoam, in most people’s minds.
Sheee-it, even the first link has Expanded Polystyrene suppliers as its first link! Yet I found all those images on one Google image search for, you guessed it, styrofoam.
Trademarked or not, the word is still subject to the evolving language rule - language is evolving, and when you can say a word and be understood, that’s what the word means. I don’t think there was ever a time when a Expanded Polystyrene bead cup wasn’t called a styrofoam cup outside of the DOW factory, no matter how much DOW wants to pout about it.