The following are presented in increasing degree of immobilization.
Guilford brace: essentially a ring around the occiput and chin connected by two posts to anterior and posterior thoracic pads.
SOMI brace: acronym for Sternal Occipital Mandibular Immobilizer. Good for bracing against flexion (especially upper cervical spine). Inadequate for hyper-extension type injuries because of weak occipital support. Has special forehead attachment to allow patient to eat comfortably without mandibular support.
“Yale brace”: a sort of extended Philadelphia collar. The most effective CTO for bracing against flexion-extension and rotation. The major shortcoming is poor prevention of lateral bending (only ≈ 50% reduced).