Here are a few ideas.

Hi RideApartians,  
I know you’re supposed to replace helmets after 5 years for safety reasons, and that if you crash in one, you should get a new one. What can you do with the old one, though? Is it recyclable?  
Thanks for your help, 
Trevor 

That’s a problem that has plagued many a motorcyclist for many a year, Trevor. Thanks for taking the time to ask. Unfortunately, the answers you find may or may not be all that satisfying. I’ve personally been looking into this question ever since about five years into my riding career, when I knew it was time to replace my old KBC and move on to a new lid. It’s now about 10 years after the first time I looked, and I’m sorry to tell you that the answers don’t seem to have changed much. 

Unfortunately, while many household recycling programs tell you to throw all different types of materials into a single bin for collection, those items get sorted by material when they get to recycling plants. Helmets are made of a mixture of materials that aren’t easily separated, and thus will likely get discarded outright if you throw them in your recycling bin. In other words, you can save time by simply binning it yourself from the start.  

Clearly, selling it isn’t a good idea, because you’ve already decided that it’s no longer safe enough for you to wear. Since that’s the case, you may also want to take the precaution of cutting the chin straps so no one else can scavenge it from your garbage bin, thinking they’ve found a good and safe helmet for free. No judgment if you’re into dumpster diving for treasure, but pulling a used helmet for anything other than art or home decorative purposes is a bad idea.  

Calling local first responders in your area to see if they’d like a donation of a used helmet is probably the most satisfying outcome. Training programs for those first responders may be able to use your spent helmet to train their people on how to handle motorcycle crash victims. If you’re going this route, leave the chin strap intact before donating.  

Upcycling your used lids into art or home décor can be fun, if you’re of a mind. If you’re into collecting lids with funky graphics, and you have the space, you could even put up shelving to simply display them somewhere in your home or garage. They may not be great at protecting your skull any longer, but they still look cool, right? Right.  

Klim currently has a program in place where it will replace certain Klim helmets you crash in, free of charge, under its Gear Protection Guarantee. You must meet certain conditions and supply ample documentation to support your claim, including a police report from the crash, in order to qualify. This information is current as of the time of writing on July 15, 2020, and may change in the future.