The buoyancy of a buoyancy vest is a key factor that determines its ability to keep the user afloat. Buoyancy is measured in newtons or kilograms and it is important to choose a vest with sufficient buoyancy to match the weight of the user. Buoyancy vests must provide sufficient buoyancy to support the user in an upright position in the water, which is particularly important in emergency situations. The choice of the correct buoyancy depends on the type of water activity and the individual needs of the user, including their body weight and swimming ability.