This large colonial casing is a popular choice for many homeowners due to its elegant and decorative design. Wood options are 3-1/4′ wide and MDF is 3-1/2″ wide. Casing is used to trim around doors and windows. It covers the gap between the drywall and the jamb. Casing is often the most prominent trim feature in your home and should be thicker than the baseboard. To increase the width and depth of the casing you can add a back band.