Styrofoam is one of the easiest materials to shape by normal means e.g. slicing with sharp knives or a hot-wire cutter, sawing with serrated blades, rasping with files, and smoothing with sandpaper. The real challenge lies in controlling the shape and especially, in this case, how one achieves concave forms. Here are the methods I’ve employed for a particular model piece which needed a ‘bowl-like’ form and very regular curves. I’ve used the standard blue styrofoam for this, in it’s most available thickness (2.5cm). There are other styrofoams, such as orange/pink or white, which are even finer and slightly denser. Like almost everything we use, styrofoam is not made for us makers specifically .. it is a roof insulation material, hence it’s not usual to find it in thicknesses less than 25mm or more than 100mm. I assume that the standard sheet size of 600x1200mm has been worked out as the most convenient for interior cladding. Go to the end of this article for advice on where to buy it in the UK.
Note to dispel any confusion, ‘styrofoam’ is the name we use in the UK for this material, officially referred to as extruded polystyrene abbreviated to XPS. Confusingly, in the US ‘styrofoam’ is the name often used for the more familiar white, packaging polystyrene properly referred to as expanded polystyrene or EPS. Both we in the UK and our American friends .. often get it wrong! .. particularly odd for the US considering it’s an American company, Dow Chemicals, who makes the blue insulation foam and who trademarked its name! So when you are doing web searches for ‘styrofoam’ make sure you know which material is being talked about before you take any advice on board. As you probably know, the two are significantly different, even though they originate from the same material! EPS is much softer, more fragile and has coarser, larger ‘cells’. Wikipedia has it basically right, with an interesting and informative article here:
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