On the surface, flotation pods sound a bit wacky: enclosed bath tubs with 30 centimetres of water and a lot of Epsom salts.
The water and room temperature are set at about 36°C – the average body temperature. You climb in, lie back and shut yourself off from the world, hopefully slipping into a state of mental and physical relaxation. At least, that's the idea.
The pods were created by American John Lilly, in the 1950s. He called them sensory deprivation pods.
He's a controversial scientist who took LSD and ketamine and also believed humans could speak to dolphins.
But Anton Kuznetsov, the owner of Auckland-based Float Culture, said he became hooked after his first float and decided to open his own business.
They're doing so well they're looking to expand, despite the $40,000 price tag of the float pods.
He said several of their clients have been with them for years.
"Others just say the weight of the whole world fell off their shoulders, they felt great for days after their float and it's just changed their life."
The scientific research on the potential benefits of flotation, however, is limited and, as Discover magazine puts it, "imperfect", given the small size of the studies done and the question over how to create a control group.
Do you control, for example, for light, sound, water or temperature? And without proper controls, it's difficult to know whether the benefits claimed come from the floating, or some other factor.
Back when Lilly was first experimenting in this area, it was described as the study of "sensory deprivation" and was associated with tales of attempts to brainwash or torture prisoners of war. But in the 1970s a new generation of social scientists renamed the experience REST (Restricted Environmental Stimulation Therapy).
But the conundrum remains. What for some is bliss, for others may be torture.
Despite claims of increased creativity, an easing of chronic pain and improved mental health, the research just isn't comprehensive. One study quoted as worthy of attention is a 2005 meta-analysis of 27 studies, which found floating was effective at reducing stress; seemingly more than relaxation exercises or slumping on the couch.
Col, a client at Float Culture, said floating had a huge effect on his pain levels and openness to life.
"It took me quite a few floats to actually get past that baseline anxiety and actually relax.
"I've struggled in the past to find psychologists, or psychiatrists, or counsellors that I connected with or that I felt comfortable enough with and safe enough with to disclose things… I'd rather work through it on my own and so it's a really good space to get that kind of observant mind."
Healthy or Hoax podcast host Carol Hirschfeld went for three floats and found they got better each time.
She said it did help her to relax, but the effects were often washed away as soon as she returned to the outside world.
"I did genuinely feel floating could allow you to experience an opening of your mind, in a very calm way, to thoughts that may normally be quite difficult," she said.
Just how well it works depends on you, according to clinical psychologist Gaynor Parkin. She points out that some stress isn't necessarily bad, but if it's dragging you down, there are many solutions including some that are almost the opposite of a flotation tank. For example, exercise or puzzles that focus the mind can help.
Parkin says if a flotation pod helps you switch off, good for you. But a walk in nature or a warm bath may achieve the same result.
Healthy or Hoax is a RNZ podcast series looking into the latest exercise, nutrition, and well-being fads to see whether there's any evidence to back up their claims. Hosted by Carol Hirschfeld.