Rooms where trim is painted.
A composite material made from sawdust and resins, ultralight medium-density fiberboard (MDF) is a stable and low-cost alternative to solid wood. It comes in a wide range of stock profiles, some with a natural wood veneer suitable for staining.
Without veneers, MDF must be painted; cutting and installing poses the same challenges as solid wood, plus ultralight MDF is easier to dent or nick.
(1) EverTrue's classic MDF ogee curves, about $15, (2) EverTrue's simplified MDF ogee profile, about $11; both through Lowes