Just What is Plasticard?
Commonly referenced in terrain articles from Games Workshop UK, Plasticard is known as Sheet Styrene in the US. It is basically dense polystyrene and is essentially the same type of plastic as you find in many plastic kits (like model airplanes).
Why is it so special?
Plasticard is excellent for terrain as it comes in many shapes, sizes and textures. You can get metal patterns imprinted on it, corrugated iron style plasticard, etc. As it is essentially thin plastic, plastic glue works perfectly and makes it easy to model and manipulate. No special considerations need to be made when painting it either. It can be easily cut with scissors or a modeling knife (depending on thickness) and it will soften when heated with steam allowing permanent bends and curves to be put in it.
Any types to avoid?
You should generally avoid glossy plasticard as it has been treated with an additional layer to remove the matte finish. This can cause paint to not stick properly, and so if you get the choice you should generally aim for matte finish plasticard/styrene sheet.
Where can I find it?
If you know of a good international supplier then add them here. One of the easiest ways to find it is to just search ebay for plasticard or sheet styrene although It shouldn't be too hard to find and most, if not all, hobby/craft shops will have at least the basic stuff.