hi, I came across the idea of using polystyrene as a moulding tool. what I figured is for certain parts 2 piece moulds might not be necessary. the part can be made out of polystyrene, wrapped with carbon fibre and once set the polystyrene can be dissolved with thinners, leaving a hopefully perfect one piece part. my question is where can I get polystyrene moulding material. im pretty sure I can buy the balls myself off the internet somewhere but that glue is used to hold it together to make boards etc...

There are kits for race car seats that come with polystyrene balls and resin, could be used for your project

I just saw on a tutorial here that polystyrene dissolves with resin. is there any other material that could accomplish the same thing

Epoxy doesn't disolve polystyrene, polyester does

thanks good to know

did the test a year ago, https://www.youtube.com/watch?v=NyF_E_jQ5o8

You can buy styrofoam board which is extruded so smooth rather than the expanded balls.  Dead easy to pattern from.

thanks lads and thanks Matt for the helpful video. how badly did the acetone react with the fiberglass resin and what was the finish like on the inside of the part? it would be easy to model with I just don't know what type of glue to use with the balls. using boards would be ok although I remember as a kid cutting it doesn't leave it smooth so again I need to know what kinda glue I need to use for touching up etc...

matt do you know if the stuff you dissolved with thinners went hard again afterwards?

You are trying to reinvent the wheel.

> the part can be made out of polystyrene, wrapped with carbon fibre and once set the polystyrene can be dissolved with thinners,

Why? Just leave it in there.

And why does everybody want to start building stuff with carbon? Start with glass.

> leaving a hopefully perfect one piece part.

Certainly not.
This is how many aircraft were made, e.g. all the early Rutan designs and their derivatives. and of course boats and yachts.

https://en.wikipedia.org/wiki/Rutan_Long-EZ
https://en.wikipedia.org/wiki/Cozy_MK_IV
https://en.wikipedia.org/wiki/Berkut_360

A big part of their construction involves sanding the microballoon-epoxy covered laminate to get something resembling a smooth surface because it certainly doesn't end up like that on its own.

The proper material to use for this is closed cell polyurethane or polystyrene foam, not the cheap insulation/packaging beady polystyrene.