HIPS High Impact Polystyrene – This is the go to plastic of choice for most vacuum forming needs. Below is the picture of its short chain. This short chain links up many times leading to a rubbery like properties. This material is very easy to heat and form and is by far one of the most forgiving materials. After molding it maintains some flexibility but can tear more easily than ABS.
ABS (Acrylonitrile – Butadiene – Styrene) Is also a great choice for vacuum forming. This has a much longer chain resulting in a very ridged structures when pulled (car components are often made of this). This is less flexible but very sturdy compared to HIPS. This is our preferred choice of materials to use (you can literally punch it with no damage to it, just a sore hand). This takes paint very well. ABS is not as easy to vacuum form and requires a more intensive vacuum to pull it properly, which is why a lot of costume-ers don’t use it. It has a longer chain and that is why it is “stronger”.