HIPS is a High Impact Polystyrene filament and has an interesting property that makes it particularly well suited as a support material - it is soluble in Limonene (easy to find on Amazon.com). If you have a dual extruder, you can print with ABS and HIPS to create structures impossible to make without support. Then, a soak in Limonene dissolves away the HIPS leaving the final part.
Very cool and the possibilities are mind boggling. It extrudes around 230°C.