The Outdoors Manual: Finding the Right Biking helmet
By Richard Luo

Do you like going fast? Do you like speeding down hills? Do you ride your bike at all? If the answer to any of these questions is "yes," then you need a helmet.
Size
The most important factor when trying to find the right helmet for you is size. The key feel when scouting for helmets is a snug, tight fit that doesn't crush your skull but at the same time is capable of preventing a concussion. Take a look at the chart from REI Co-op to find your helmet size based on head circumference (measured in centimeters)

REI Co-op corroborates that the best way to measure your head circumference is to wrap a string around the top of your forehead then measure the length of the string.
Types

There are many types of helmets for bikers that ride on different terrains. An extremely popular helmet for recreational bikers and amateur mountain bikers are lightweight, microshell designs similar to the Schwinn Thrasher Bike Helmet. On platforms such as Amazon or eBay they cost around $20-$30, which is a moderate price. They are designed to not only be lightweight, but also entail 20 air vents that provide crucial ventilation - especially in blazing summer temperatures. Additionally, a defining characteristic of the helmet is the polycarbonate plastic visor located at the front of the helmet. The visor has multiple purposes including shielding against sunlight, rain, splashing mud, and low hanging branches that may gouge your face. These type of helmets are usually able to protect you from major falls such as flipping over the handlebars of your bike or landing on concrete. However, often times they break or crack in the process leaving you no choice but to buy a new helmet.

A more obscure type of helmet that most people find in movies are Full Face Mountain Biking Helmets. At a relatively high price from $50 to a few hundred, it provides full coverage of your countenance and many people choose to wear goggles as a complement. Full face helmets have many similar properties that align with regular biking helmets. The Demonic Podium Helmet features 13 massive air vents, lightweight construction, and even the same polycarbonate plastic material. In addition to comprehensive protection, many mountain bikers also utilize these helmets for style with customizable graphics and designs.
Many people don't realize the importance of finding the right helmet or even wearing one in the first place. Studies have shown that helmets are the single most effective way to prevent deaths and injuries in activities far more dangerous than biking - most notably motorcycling. Even though you don't need to obsess over finding the perfect helmet, it's important to spend 5 minutes doing some research that may prevent 5 days in the hospital.