The best bull riding helmets are the ones designed by bull riders for bull riders. These are the guys who know the game and understand where the most potential for injury exists. Eight Second Rider also has some more info on this.

A good, serviceable bull riding helmet features:

adequate jaw and facial protection,
smooth contours,
durability,
light weight,
snug fit,
and breakaway capabilities

Helmets that are certified by the ASTM, or American Society for Testing and Materials, have been rigidly tested and approved to help save your life when you come eye-to-horns with one ton of furious bovine.

Adequate Jaw and Facial Protection

Wearing the right helmet can mean the difference between a simple wired jaw and major reconstructive surgery. A good bull riding helmet has a facial cage similar to a hockey helmet, but the similarities end there. The openings on a hockey mask are large, letting regulation-sized horns fit through. A helmet specifically designed with bull riding in mind features smaller openings in the interest of keeping horns away from the rider's face.

Smooth Contours

In the past, riders who opted for the protection of hockey masks paid the price when the bull's hooves caught on protruding areas of these types of helmets. The designers of genuine bull riding helmets have taken this into account by giving them sleek, smooth outlines that tend to deflect the blows, instead of absorbing them. A glancing hit from a hoof that slides right off is much more sustainable than being hooked by your helmet and tossed.

Durability

Some of the best bull riding helmets on the market were designed by tapping the input of military and flight engineers. Materials such as Kevlar, carbon fiber, and titanium provide superior protection against fractured skulls and debilitating facial injuries. Look for helmets that incorporate these types of materials when comparing brands.

Lightweight.

Weight is a major concern for any bull rider, but especially to those new to wearing a helmet. Bull riding takes concentration and focus, and suddenly having a heavy helmet weighing you down can be dangerous. Luckily, thanks to military technology, some of the toughest materials used in bull riding helmets are also the lightest weight. Always take the weight of a potential helmet into account before buying it.

Snug Fit

A bull riding helmet that dislodges into the atmosphere at the first buck of the bull won't be much protection when you're on the ground. The chin strap must be significant enough to withstand all the jolts and hits that accompany the sport while still breaking away if the bottom of the helmet becomes hooked on a horn. The helmet should be adjustable to fit close and snug to your head. At least one type of helmet on the market today uses a type of reinforced memory foam inside the helmet that learns to conform to the shape of the rider's head. This type of helmet gives a superior fit.

Breakaway Capabilities

Having a headgear that breaks away under extreme pressure is actually a good thing for a rider who's had the misfortune of getting hooked under the helmet by a horn. The better helmets are designed to break away when extreme upward force is applied to help prevent riders from literally losing their heads. Some helmets also come with emergency clips that allow medical personnel to remove the front of the mask without moving the injured rider's head. These are both vital features to look for when purchasing a bull-riding helmet.

More and more professional bull riders are turning to the security of helmets designed especially for the sport, according to Professional Bull Riders.

… written by Ken Tabor, a Bull Riding Fan and Internet entrepreneur.