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Common packaging styrofoam is actually puffed polystyrene, the same polymer that’s used to make things like CD cases and plastic model parts. When acetone is used as a solvent, the expanded polystyrene will easily dissolve and you’ll be left with a liquid acetone/polystyrene solution. As the acetone evaporates, the polystyrene becomes increasingly viscous: first pourable, then moldable, and finally solid polystyrene plastic.

Solid polystyrene will dissolve in acetone as well, but with the vastly larger surface area (due to all the little gas bubbles) styrofoam dissolves much faster. That, and it’s readily available if you have a basement full of old packaging materials.

There must be an easy method for pouring or spin-casting custom plastic parts or action figures using dissolved polystyrene. Have any of you ever tried this or have any ideas on the subject? Please let us know in the comments!

Instructable: How to “make” plastic – Link
Wikipedia: Polystyrene – Link



  1. mrChew says:

    remember that that stuff has a lot of nasty stuff in it. you should definitely be wearing a full respirator, thick gloves and have adequate ventilation to prevent the buildup of fumes (and possibly a house fire if the water heater kicks on at the right moment!) remember, you only get one body – TAKE CARE OF IT!!

    there’s actually an easier and probably less toxic supply for making plastic parts. hobby stores carry a clear two part resin used for casting the clear plastic bricks (usually with a butterfly inside). it’s about $5 for enough resin to make an actual brick sized chunk of plastic.

    that being said, you can make a mold out of anything that wouldn’t be dissolved by acetone. balsa wood would be a great choice, as would (cured)fiberglass or even plaster(really cheap at either the local hardware store or the hobby store). making plaster molds is extremely easy, and -apart from the dust during mixing- very non toxic!

    heres a link to a manufacturers web site with a PDF manual for making plaster molds:

    there are plenty of other guides out there, just search for “plaster mold making”

  2. ordaos says:

    I electrospin viscous polystyrene solutions as part of my graduate research, creating fibers on the nano scale, from 30nm to 10um. These fibers end up looking a lot like cobwebs, something most people try to get rid of.

    Drop casting, spin casting, or molding are probably more tangible and useful fabrication methods. You could also use this stuff in a fab@home if you happen to have one of them lying around.

  3. PhaseShifter says:

    mrChew said
    remember that that stuff has a lot of nasty stuff in it.
    Are you sure you’re not thinking of polyurethane foam instead of styrofoam?IIRC, polyurethane is formed by reacting isocyanates with water, and is used where you want to expand the foam in place. The downside is a lot of toxic materials, the upside is that it gives you one or two custom-fit solid blocks of foam instead of small bits that end up everywhere when you unpack.

  4. jswilson64 says:

    That’s an old modeler’s trick. The sprue or parts “trees” can be dissolved in acetone or liquid model cement to make a filler that has the same properties as the model. So it’s no more or less resistant to sanding, etc.

    This “liquid” plastic could have a zillion uses as a rapid prototyping material, “oops” fixer, etc. Just make sure you’re working in a well ventilated area! Oh, and after enough exposure to it, acetone and lacquer thinner cause my skin to break out…

    1. Sivadasan says:

      Dear JS

      Are you taking about Polystyrene/ Acetone slury pouring into a mold to get a plastic article.

      Give me more clues.

      Prof. Sivadasan

  5. Stunmonkey says:

    We used to dissolve EPS into gasoline to get it viscous and sticky for firebombs, so acetone isn’t the only solvent that will dissolve styrofoam pellets.
    I never thought of what would happen to the polystrene after the solvents had evaporated though. Could be useful for making parts in a pinch!

  6. Dave Sutton says:

    bake-able plastics are available at hobby shops and craft stores.

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