Instructables
Picture of Designer vases from used coffee cups
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Styrofoam cups are light, cheap, and insulating, but flimsy and rarely recycled. Here's a way of transforming a used styrofoam cup into a similarly-sized vase of your own design. It costs nothing, only takes a few minutes, is ridiculously easy to do, and every vase/pot will be unique. It's an interesting gift if you add flowers or a small plant.
 
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Step 2: What and how

Styrofoam is a brand name for expanded polystyrene (a hydrocarbon polymer blown full of gas). Put a styrofoam cup under high pressure and/or heat and it will shrink dramatically as the gas is driven out. You can do this by putting the cup in a submersible ROV and sending it 1400 m underwater, or much more easily, by popping one in a pressure cooker for half an hour - you'll get a neat miniature coffee cup. It's cute, but not much good for anything (espressos?). The photo above shows how when you heat the coffee cup, it first expands, then shrinks smaller and smaller the longer you leave it. It also gets somewhat distorted, because the plastic gets quite soft. I did these in the slow cooker, but you get a more perfect little cup in a pressure-cooker (see the second photo - it's also faster).
Whether you're making tiny cups or making funky vases of your own design, get the cooker up to heat first (on high). It's also important to cook the cup bain marie style, i.e. inside a bowl that is immersed in water. Otherwise, you'll just melt the cup and make a stinky mess of your cookware.
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ikurniawan25 months ago

very nice

NikkiDread10 months ago
When I was a kid we used to decorate the cup with markers first then put it in the oven. we made small hats for dolls with them for 4th of July
makendo (author)  NikkiDread10 months ago
Neat. How long did you put them in for? How small did they get? You should write it up, sounds fun.
MYT CR8TiV1 year ago
Will this work in a regular like soup pot with a lid ? My husband always brings home Styrofoam cups from work and I always wanted to find ways to craft with it. This seems interesting enough to try.
makendo (author)  MYT CR8TiV1 year ago
Sorry for the *really* slow reply... yes, it would work fine. calischs made a video instructable which showed it working just by dunking a weighted cup in a boiling pot of water.
sabu.dawdy1 year ago
how do u doooooooo this shuff.. its awesomeeeeee
It's called... Read and find out
hahaah
shortone1 year ago
Great idea! I have once concern though: I know that melting styrofoam is super toxic, which is why it is a very bad idea to use a wire cutter on styrofoam at all. Do you know anything about the toxins released by heating it up in water? I don't know myself, but I'd definitely want to research it a little more before I melted too many cups! :)
makendo (author)  shortone1 year ago
Probably the same amount of toxins released as when adding a hot coffee to the cup, i.e. very little. The water is at 100°C or just above, and while it's clear the air in the polystyrene is driven out over time as the cup shrinks, that's all you really need to worry about. You're not melting the cup.
Oh my! I'm glad I didn't miss your instructable. The heading~what to make with garbage~almost put me off. Garbage or trash. Food or other. This is one our grandson and I will definitely try.
taria3 years ago
these are pretty cool, to bad spray paint eats them up like candy, cause if you added some of that textured spray paint to them they would look like little stone planters...oh wait, when they are shrunk down you think spraying them with paint would still eat them since they aren't so 'puffy' anymore?

I won't be able to try this cause my mom would kill me if I used her pressure cooker for shrinking down cups. I know I feel like a 4 year old when I'm not. Might have to just go out and buy my own just to try this. :)
makendo (author)  taria3 years ago
I suspect the shrunken cups will still get chewed up by the spray paint.
It is a pretty frivolous experiment, to be sure, but I think you're overestimating your mom's reaction. She's more likely to think they're cute than be driven into a homicidal rage... but I don't know your mom. :)
Yes. The solvents in the paint will still eat the styrene. Your choices are model making paint (maybe) or acrylic paint like that found in Primary Schools.
Wonder about a Sharpie?
good idea, I didn't think of acrylic paint. thanks for that.

and makendo, my mom would have a cow trust me, so I will do this at my own house with my own pressure cooker...lol
Sooo, soo cooool! I have too much stuff around, so I probably won't try this for a while, but what a great idea!!!!
corinalex2 years ago
Cool! My daughter and I will be recycling lots of cups this way. Thanks.
This is adorable and I can't wait to try it.
raviolikid2 years ago
Do you know how long it takes water to boil in a slow cooker? Or, could I use a pot on a hot plate? I think this is an interesting project for my students in my Arts and Engineering Clubs. I like the maker who make concrete forms with them. We might try that, as we are studying concrete in the fifth grade group.

Thanks!
makendo (author)  raviolikid2 years ago
Pot on hot plate will work fine, as long as you have a lid.
Great! I have lids!

Thanks for your reply and for the cool Instructable with the great links! I mean, your directions were great - but adding the links was a nice bonus.
goes great with the "coke can flower"
csantiago33 years ago
This is very cool, now to find syrofoam cups!!
I had no styrofoam cups so I used a styrofoam bowl. I put only one rubberband and it came out to be a hat after 10 minutes. :) Here is what they look like
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makendo (author)  rojo.balloon3 years ago
Nice styrofoam hat! Thanks for posting the pictures, good to see it works for bowls too.
This is a pretty fancy idea :0) I will definitely be trying this! Thanks so much for taking the time to share this unique technique. Have a wonderful day ^.~
makendo (author)  TheNailDutchess3 years ago
You're welcome, & good luck.
WhyHello3 years ago
I'm curious how did u get this idea :)
makendo (author)  WhyHello3 years ago
I knew that you could get a miniature polystyrene cup by pressure-cooking it. I wondered what would happen if I used a slow cooker instead, and the rest was just messing around...
WhyHello3 years ago
I wonder if you can use a microwave
makendo (author)  WhyHello3 years ago
Probably not. Microwave ovens work their magic on water, and a styrofoam cup doesn't contain much. However, if you added water, put bands on the outside, and cooked it for a minute or two, who knows? You should try it :)
ellequoi3 years ago
Neat! I wonder how these would work as little planters if you poked holes in the bottom. I'm kind of concerned about the chemicals that would wear off on the pot as well... maybe this would be something I'd try with a reject pot, or a crockpot with a liner added.

Also, would dye in the water stain the cup for you?
makendo (author)  ellequoi3 years ago
Thanks. They work just fine as planters, but they're kind of an awkward shape.
Any leaching of blowing gas, assuming there is any left in there, will be minuscule - you'd expose yourself to far more toxic chemicals by eating any blackened piece of food. Or a peanut. Or an apple seed. Or lighting a candle. Or painting something. Fortunately, we have all sorts of clever mechanisms for scavenging small amounts of toxins out of our system - just as well, or smokers would have to worry about a quick death from cyanide poisoning as well as a slow one from cancer. The gas used to foam polystyrene is volatile, so if you want to be super-cautious, just do it outside. It won't stick to the pot.
Any dye that dissolved in the water would not stick to the cup, unfortunately.
Bunchland3 years ago
We loved this idea so much we thought we would share it with our readers as well.

http://www.bunchfamily.ca/valentines-day-craft-styrofoam-vases-paper-flowers
makendo (author)  Bunchland3 years ago
Thanks for letting me know - good idea to include the video.
I was wondering if you could manipulate the shape even more by putting the cup on a turntable/lazy Susan and using a heat gun. Then, you could heat the cup in specific places. I have one for heat embossing when I rubber stamp.

If I get hold of any styro cups, I'll let you know what happens.

Suzanne in Orting, WA
I know that styrofoam melts almost instantly against the tip of a hot glue gun (personal experience) so it might just create holes in the cup.
I'm sure it would melt the styrofoam if it was held too closely, especially if it was a industrial strength type gun, but the one In have is a basic rubber stamping type and I think if enough attention in paid to the distance, it will be do-able. In fact, I never thought about using the the heat gun to melt holes in the foam. It could be an interesting addition to the textures.

Since I have sheets of foam, I was thinking about cutting them in circles and using the gun to raise the edge of the blanks to create "plates".

Thanks for the additional ideas!

Suzanne in Orting, WA
makendo (author)  Suzanne in Orting3 years ago
Interesting idea; don't be surprised if your cup goes all Salvador Dali on you! Good luck, I look forward to hearing about the results.
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