Black KAPA graph foamboard.
Premium foamboard that has a unique polyurethane foam core which doesn't crumble or flake when cut. Use for all creative art, backing photos, posters, pictures, presentation and many uses for model making and prop work.
The core is not really completely black (for reasons of production technique it is only very dark grey). If that bothers you, you can always go to a black foamboard but bear in mind the disadvantages of polystyrene rigid foam cores (these include a less than perfect plane for layouts, more crumbling when cutting, not resistant to solvents).