Donate your old helmet to an organization that collects bicycle helmets, if there is one in your community. This is best for children's helmets that were rapidly outgrown, as you can only donate helmets that have been very lightly used. Donated helmets should be relatively new and have never been involved in an accident or collision.
Remove the foam lining from the inside of the helmet. Crumble this foam into pieces and use it as packing material or as a soil enhancer.
Cut off the helmet's straps with a pair of sharp scissors. Dispose of the straps and buckle in your regular trash.
Examine the remaining plastic shell of the helmet for a plastic recycling symbol. If the helmet carries a recycling symbol with a number inside it, contact your local recycling agency to ask if they accept that type of plastic for recycling. Recycle in your curbside recycling bin or at a recycling center, if possible. If not, dispose of the helmet in your regular trash.