Styrofoam square "project boards" from Lowes - Scored for texture.
Lab pieces randomly from various McFarlane sets
As I've tried hard to incorporate dioramas and playsets into my customizing, as well as to continuously improve my skills towards them, I inevitably ended up working with foam insulation pieces.
They are so easy to cut and manipulate, and can be used to make many different real life textures as a result.
This simple wall and floor can be used for all sorts of scenes now, and I plan to add extra walls, for shooting from different angles. They are also modular.
I credit artist Stephen Hayford with inspiring this set as well as others.