I fixed my helmet with sew-up glue and a sock
Partly because throwing it out would be a waste of syrofoam and partly because I am a cheap bastard.
Sometimes going green and being frugal are the same thing.
One of the straps that hold the black plastic piece to the back of your head came loose, so I glued it back on. The sock I put there to clamp it until the glue dried, then trimmed the excess so that part of the sock is stuck there and protects my head from the excess glue.