First, you'll have to separate the materials. The straps will be pitched, nylon is not easily recycled. The hard plastic bits can probably be put into your recycle bin and your recycler can sort them out. The bulk of the helmet, the foam part is expanded polystyrene. There are not a lot of places that recycle that, here is a list.

http://www.epspackaging.org/pdf/AFPR...ions112907.pdf

They also may not want your helmet because it has pigment in the plastic which makes it less desirable to recycle.