The Claim: The practice of regularly floating in a special tank full of warm water and Epsom salts can profoundly relax a person and lead to a variety of mind and body benefits, according to centers that charge for sessions in the tanks.

The Verdict: Regularly floating in such tanks has been shown in research studies to reduce stress and anxiety, ease back and fibromyalgia pain and improve sleep. But the studies are mostly small, and larger, rigorously designed trials are needed, scientists say.

Floating, pioneered by the late neuroscientist John C. Lilly in the 1970s, fell out of favor in the 1990s and is now back, says Lee Perry, president of Samadhi Tank Co. Inc., a Grass Valley, Calif., company. There are now 267 float centers in the U.S., up from an estimated 85 in 2011, according to Aaron Thomson, chief executive of Flotation Locations, a Brick Township, N.J., company that runs a website that lists flotation centers. A 1½ hour session generally costs $45 to $100, he adds.

Tanks vary in style and price. The classic style, such as the boxlike plastic model from Samadhi, is intended to be dark and silent and can be had for as little as $6,000 to $15,000. A newer style, called a pod, is made of fiberglass and has doors that open and close like the back of a sport-utility vehicle. A $22,500 model from Float Pod Technologies LLC of Tempe, Ariz., offers a choice of six colors of light and a music dock. It can be used with the lid open, making it a good introduction for someone anxious about being enclosed, says Alden Witte, company sales director.

Hundreds of pounds of Epsom salts are added to the tanks to make the user particularly buoyant. The water is heated to skin temperature, or 93.5 degrees Fahrenheit, companies say. The tanks are filtered between each use and disinfected with ultraviolet light or other methods, depending on the company.

Click for more from The Wall Street Journal.