A length of warm, soft fabric (fleece is nice since it doesn't fray)
Elastic
Measuring tape
Scissors
Thread
Sewing Machine
Step One
I made this to fit my 18 month old daughter, so I cut the fabric to measure 20x8". For an adult, I would make it about 35x10", depending on the head size.
Cut TWO pieces of this fabric in the same size.
Step Two
Cut the elastic about 3" inches shorter than the length of fabric. Since my fabric was 20" long, I cut the elastic at 17".
Sew the end of the elastic onto the end of one of the fabric lengths, right in the middle, then sew the other end on as well.
Step Three
Place the second piece of fabric over top of the piece with the elastic. Sew both ends closed.
Step Four
Sew a seam along each side of where the elastic lays, about 3 inches from each edge.
Step Five
Cut triangles out of each edge, right up to the seam.
Step Six
Turn it inside out, and there you go. I love the way the triangles frame my daughter's face -she looks like a little flower (or maybe a jester...).