During much of the 18th century, women wore bonnets whenever they left the house, so a bonnet is an essential of any costume depicting this era. A cardboard bonnet is inexpensive to make, but it can still be attractive. Spray paint it to match your outfit, and use attractive ribbon for the ties. Decorate the outside with ribbon and feathers, or glue ruffled trim or silk flowers inside the brim to draw attention to the wearer's face.
Measure the height and width of the back of the wearer's head using a ruler. Use a tape measure to measure the distance over the wearer's head. Measure from her chin on one side, over her ears to her chin on the other side. Measure the distance from the back of her head to the desired location of the bonnet's brim, using a ruler.
Draw a rectangle the height and width of the wearer's head on cardboard. Round the top of the rectangle to make a horseshoe shape. This will be the back of the bonnet. The distance around the top and sides of this arch should equal the distance over the wearer's head. Add to the length or width of the back, if necessary.
Cut out the back of the bonnet, using heavy shears or a mat knife.
Cut out the sides of the bonnet from poster board by cutting a rectangle, using the distance over the head and the distance from the back of the head to the bonnet brim.
Wrap the long edge of the bonnet's sides around the bonnet's back. Duct tape it in place. If either piece is a little too long, trim it so the edges are even.
Spray paint the bonnet inside and out.
Cut two 15-inch pieces of ribbon. Cut one edge straight across and the other at an angel to prevent fraying. Fold under 1/2 inch on the straight edges. Staple these edges to the bottom front corners of the bonnet. If desired, glue a band of ribbon or some feathers to the outside of the bonnet with a glue gun. You can also add ruffled trim or silk flowers inside the brim of the bonnet to frame the wearer's face.
Spray paint in a well-ventilated place. Protect the surrounding surfaces from spray.