Abstract: Methods, systems, and apparatus, including computer program products, for representing reinforcement. A three-dimensional (3D) solid object in a computer aided design (CAD) model is identified. The solid object has a volume. A reinforcement element is associated with the solid object. The reinforcement element defines a path within the volume, occupies no space in the volume, and has a width value greater than zero. The reinforcement element is rendered as a ribbon having a width and having no volume. The width of the ribbon is the width value of the reinforcement element. A view of the solid object, including a view of the ribbon, is presented. The width of the ribbon is orthogonal to a direction of the view of the solid object.