Look for housings made of strong and rigid materials. The two most common materials are aluminum and polycarbonate. Other acceptable materials are polyurethane composites and ABS. Don’t bother with bag style housings. They are cheap, but aren’t well suited for diving and provide little physical protection to the camera.
Aluminum housings are usually the most durable and have the highest depth rating, typically 330 feet. They are also the most expensive since they require a lot of machining to make. The prominent makers of aluminum housings are Amphibico, Gates, and Light and Motion.
Ikelite is the most known maker of polycarbonate housings. Polycarbonate is a durable thermoplastic. It has the advantage of being clear. Thus, you can easily see inside the housing and quickly spot any leaks. Polycarbonate housings are much less expensive than aluminum housings and can safely operate to depths of 200 feet.
UnderSea Video and Ocean Images make housings with polyurethane composites. These are durable yet lightweight and are safe at depths from 200 to 250 feet. Sea and Sea manufactures housings from ABS plastic resins that are rated to depths of 200 feet.