This instructable details the making of a soft quilted tetrahedron costume for the more patient of my two cats.
Step 1: Choose fabrics and preprocess them
You'll also need an attractive color of quilt binding. Binding can be purchased at most fabric stores (I use Joanne's). The binding is a cloth strip that will sandwich the outer hem to create a finished edge. Also make sure you have a color of thread that matches your fabrics.