A three-dimensional printer is configured to fill interior cavities of a fabricated object with functional or aesthetic materials during fabrication. In general, a number of layers can be fabricated with an infill pattern that leaves void space within an exterior surface of the object. These void spaces can receive a second material such as an epoxy or adhesive that spans multiple layers of the object to increase structural integrity. Similarly, aesthetic materials may be used to add color, opacity, or other desired properties to a fabricated object. The void spaces can also or instead form molds that are filled with a build material to provide a fabricated object.