Most bicycle helmets are constructed out of foam, which absorbs impact quite well. But if you want more protection for your precious fragile head, you can either use a motorcycle helmet or something a bit more practical like the Smith Optics Overtake Helmet. It uses a material called the Koroyd polymer core, proven to absorb 30% more impact than the typical foam and is constructed in a way that reduce forces to the brain in case of an oblique impact.
$250 Buy