Crash helmets or motorcycle helmets are designed to protect the users from head injury.
Wearing a helmet when riding a motorbike is mandatory in the UK and they have to be designed to comply with safety and build standards.
Since the introduction of helmets, they have reduced head injury by nearly 70% and death by over 40% they have even believed to have reduced spinal damage.
Helmets can vary in design from open face pudding basin shape to full all round enclosed helmet with a visor like this one.
This helmet also includes vents and a drop down internal sun visor.
I don't own or ride a motor bike I purchased these helmets for part of a set of sci-fi space suits costumes as below.
Interesting fact (maybe) wearing a white helmet reduces your chance of road accident by 25% compared to a black helmet, is that because those with white helmets are the more sensible road user or because they can be seen easier?