There are many types of indoor surfaces that use a carpet base. Different carpet weaves, pile heights, materials, sand fills, clay fills, etc. Also different sub bases that affect the softness of the surface.
Usually they are designed to simulate grass or clay.
Im assisting in a project for 6 courts and the choices are many.
Current & recent affairs: PS97 (coming soon!), ai98, Extreme Pro 2.0, Steam 99s, PK QT 295, Dunlop 3.0T & Bio 400T