The exterior is constructed with Professional’s Choice signature limestone-based neoprenee, 4-way stretch conforms to your horse and provides suppocrt for the suspensory system. With an UltraShock™ lining, it also provides 360 degrees of impact protection and helps prevent fetlock hyperextension. SMB IIs® have protected countless performance horses over the years in every imaginable event. For many horses, these boots have meant the difference between an extended career and periodic or permanent injuries.