Which is correct, moulding or molding?

Both spelling variations—moulding and molding—are considered entirely correct and grammatically acceptable, with their acceptance depending primarily on geographic location and regional spelling standards rather than strict rules. Moulding, which includes the letter u, is the standard and traditional spelling widely utilized across the United Kingdom, Australia, New Zealand, Canada, and other regions that adhere to British Commonwealth English guidelines. Conversely, molding, omitting the u, is the standard spelling preferred throughout the United States within American English dictionaries, architectural literature, and building supply industries. Because both terms refer to the exact same decorative millwork and manufacturing processes, writers and contractors can choose either spelling with confidence, provided they maintain consistent usage throughout their documents to match their local audience.