Some of the more expensive helmets have better ventilation, better shell material (some up to carbon fiber). Make sure the liner is removable so you can wash it, and you have extra shields, since manu manufacturers stop making replacement shields so you replace the helmet after a couple of years.
If you're thinking of buying online, first go try on helmets in a store to make sure it is comfortable and it fits right. I have one where the face flips up (called modular helmets), but they do not have good Snell ratings. Mine popped open once at highway speeds, annoying but not bad. Make sure you latch them securely. I have an HBC full face helmet. If I were going to buy another one, there's a company that starts with an 'a' with an Italian flag - good helmets and comfortable.
If you're thinking of buying online, first go try on helmets in a store to make sure it is comfortable and it fits right. I have one where the face flips up (called modular helmets), but they do not have good Snell ratings. Mine popped open once at highway speeds, annoying but not bad. Make sure you latch them securely. I have an HBC full face helmet. If I were going to buy another one, there's a company that starts with an 'a' with an Italian flag - good helmets and comfortable.