The construction of waterbeds improved to eliminate the risk of puncturing or bladder leakage. Bladders are made from heavy-duty vinyl and in most cases are enclosed with a safety, waterproof liner for additional protection. The vinyl should be at least 20 millimeters thick, although there are some models with up to 30 mm thickness.
To control the temperature of the sleeping surface, waterbeds either use a built-in electric heating pad placed directly under the bladder, or use a thermal layer to protect and insulate the body.
Waterbed bladders come in different levels of depth, sometimes referred to as fill levels. They come in 3-5 inches (shallow), 5- 6 inches (mid-fill) or 7- 8 inches (deep fill). Shallow fill bladders are usually used only in soft-sided waterbeds, with padding layers of foam on the top providing additional comfort.