The primary component of all weight systems is lead, which is so heavy and dense that a small amount easily offsets your positive buoyancy. The most common and basic weight system is a weight belt. Weight belts are typically made from a 2" wide piece of nylon Webbing which threads through lead weights designed specially for SCUBA. Some weight belts have compartments or pockets, which hold "soft weights". Soft weights are sort of like beanbags filled with lead shot. These have become quite popular as they tend to be a little more comfortable the "traditional" belts. Additionally some newer Buoyancy Control Devices (BCD) have an "integrated" weight system so a belt is not even necessary. 

Whichever system you choose, the weights MUST have a quick release feature to allow immediate removal with one hand. 
 

A startling fact: At least 80 percent (some reports put it as high as 100 percent) of divers who die while in the water do so without ditching their weights. At the same time, it has been clearly demonstrated that achieving positive buoyancy can quickly change a possibly fatal accident into a near miss. The bottom line: The inability and unwillingness to ditch weights costs lives. 

Part of the problem is that many divers view weights as a necessary evil, a burden to be tolerated, rather than as a vital piece of dive equipment, as important as a mask or fins. Weights are key components in a diver's total buoyancy control system. They are needed to achieve positive, negative and neutral buoyancy; to provide balance and stability; and, finally, to give a reserve of positive buoyancy during emergencies when they are ditched. Like any piece of gear, using weights effectively and safely to achieve those purposes requires knowledge and, most of all, practice.

To appreciate the complexity of weight systems and the need for training in how to ditch weight, just consider the many problems that can occur in their use. Problems shared by the two primary weight systems in use today - weight-integrated BCs and weight belts (sometimes accompanied by harnesses and shoulder straps) - include: 

• Over-weighting and under-weighting. These problems occur most often with divers who don't understand the importance of buoyancy checks or how to perform them. 
• Loss of buoyancy control. The inability to maintain buoyancy control throughout a dive is a major contributor to dive accidents. 
• Failed attempts to ditch. This can be caused by the need to be nearly vertical to ditch effectively, the difficulty in ditching with cold or gloved hands, or poor ditching technique. 
• Incapacitation. Some divers are unable to ditch due to fatigue, heart attack, air embolism or other malady. 

Problems specific to weight-integrated systems include:

• Inability to use the system's ditching mechanism effectively. This applies to divers who don't know how their own weight systems work, as well as to potential rescuers. 
• Poorly functioning weight systems. ScubaLab tests have shown that the failure of weights to drop when released can result from poor design, overloading of the weight pockets or the position of the diver. 

Problems related to weight belts include:

• Inaccessible buckle. This occurs when a loose belt rotates so that the buckle is no longer in front or when the belt is covered by the BC. A fully inflated BC can also prevent the diver from reaching the buckle. 
• Entanglement. Other gear in the drop zone such as gauges, knife, alternate air source, goody bag, even fins can entangle the belt. Weights are also sometimes rigged on the belt so that they are caught under the BC/tank combination and held in place. 
• Faulty buckle operation. This can be caused by belt webbing that is so long it will not pull clear of the buckle, a buckle that doesn't stay open during ditching, weights so close to the buckle that they interfere with its operation, or a misthreaded buckle that will not release.