Whether you are creating a craft statue of a bird, a bird mask, or a full bird costume, foam can be a great tool to make a three-dimensional bird beak. Creating a foam beak, however, requires a steady hand and a lot of patience--you may need multiple attempts before you create a foam beak that most accurately and satisfactorily represents the beak of whatever bird you are creating. Prepare carefully and perform research for the project before beginning.
Study different pictures of the beaks of the type of bird you are creating, be it a mask, costume, or statute. The shape, size, and proportion will vary widely based on the bird; the shape of a chickadee's beak is completely different from that of a toucan. Your bird beak may also vary based on whether you are creating a male bird or a female bird. Studying pictures of different beaks gives you a good feel for the type of beak you want to create. In general, the more triangular the beak, the easier it is to create.
Sketch your desired bird beak, to scale, on a piece of scrap paper. This helps steady your hand when you go to draw the beak on the craft foam, and gives you a good feel for the necessary curve angles of the beak.
Cut a piece of foam into a cylinder, roughly equal to the base-to-tip size of the beak, using scissors.
Using a pencil, draw a rough sketch of the beak on the foam, delineating where you will cut.
Carefully cut the foam along the designated lines. Begin with the top of the beak, slowly working your way to the tip, then cutting the curve of the under-beak. You may want to start by creating a rough beak shape, then slowly use scissors to trim the beak to the desired shape.
Use paint or markers to add details to the beak.
Work carefully when using scissors to cut three-dimensional objects at an angle.