The primary material used indoors is GRG. GRG is a gypsum based product (like drywall) which makes it easy to install and finish. Curved surfaces and detailed profiles are ideal for GRG.
Typical interior products include:

Column Covers
Pilasters
Decorative Moldings
Cornice
Ceiling Domes & Vaults
Light Reflectors
Light Coves
Acoustical Clouds
and more...