What do you think about foldable helmet?
There are so many of them but here are some examples.. personally, I just carry my helmet with my hand but if I had an option to put in my backpack it might also be useful..
https://www.morpherhelmet.com/
https://closca.com/products/fuga-helmet?variant=53832191509
https://fend.io/
https://www.overade.com/shop/en/plixi#/2-taille-m/14-color-blue
There are so many of them but here are some examples.. personally, I just carry my helmet with my hand but if I had an option to put in my backpack it might also be useful..
https://www.morpherhelmet.com/
https://closca.com/products/fuga-helmet?variant=53832191509
https://fend.io/
https://www.overade.com/shop/en/plixi#/2-taille-m/14-color-blue