Above is a "Jazzy" shower bonnet. It is lined in a green re-cycled plastic bag, with a nylon lace overlay, and fun ribbon scraps and odd buttons rummaged from notions box. Below is another version, this one made from an old vintage, polyester California State scarf. 
These bonnets take an hour maximum to make, and are so practical and fun - and decorative and cheery in the bathroom. This is how you sew them... 
Gather together your materials - above, is a vintage polyester scarf, a green plastic bag pulled from the re-cycle bin, 1 yard of 1" wide turquoise gingham ribbon + (not in the photo) 1 yard of 1/4" wide elastic, 1 yard of 1" wide yellow gingham ribbon, red thread.Directions:
Cut the scarf in a circle, with a 20" diameter. Repeat with the green plastic.
With wrong sides facing, align the two circles together, and stitch all around, 5/8" from the edge.
Sew the turquoise ribbon around the edge.
Make a casing for the elastic with the yellow ribbon. Align the yellow ribbon 1/2" from the edge of the turquoise ribbon. Stitch with a zigzag stitch, 1/2" from the edge. Stitch a second row, 1/8" from the other edge, leaving a 2" gap to pull the elastic through the casing.
Slip the elastic through the gap, pulling it through, pin the ends to together, to an ease that is comfortable for your head. Stitch elastic closed, and clip excess.
Fold back excess ribbon to form a bow, and tack with a button, or two.
Enjoy!