Building foam help


Hi all just got a question, I'm planning doing some new builds and have seen some amazing stuff made from foam, but was wondering what's the best foam to use? Plus any type of plastic building material out there that's good as have used some stuff but it's not good to work with. Oh by the I'm in the uk but if any of you guys can recommend some good stuff to use that would be great help thanks.
Well not sure whats available in the UK, but i use Urethane foam. also it depends on what you want to make. i use different foam for different applications. softer foam for quick vac paterns and a more denser foam for parts that have more detail. as for plastic theres always Styrene which is great for anything vacforming and parts and i use Sintra for larger more stable parts.

Would help to know what exactly you want to make to pick a foam or plastic?