A bonnet is NOT a kapp. The kapp is a religious head covering, worn always. The bonnet is practical, worn over the kapp outdoors.
Purpose
Sun protection (Amish women work in the garden for hours). Rain protection. Protects the kapp (white kapp gets dirty outside). Warmth in winter.
Construction
Rigid frame of cardboard or plastic. Covered in black fabric. Wide brim in front (sun visor). Ties under chin. Soft back section covering the neck.
Types
Summer: more open, breathable. Winter: insulated, covers ears. Travel: largest, for buggy rides (wind, dust).
Shape = Community
Like the kapp, bonnet shape tells where someone is from. Lancaster: rounded, medium. Indiana: elongated. Ohio: small, compact. A knowledgeable Amish person identifies the community in a second.