How much for that tin foil hat?

Products that block electromagnetic waves are becoming a big business as a growing number of people look for ways to protect themselves from the ill effects of technology.

From paint and tents to hoodies and socks, makers of products that claim to block harmful electromagnetic fields are on the rise, sellers say. And it’s not just people on the fringes who are buying — or selling.

Twitter Chief Executive Jack Dorsey recently revealed that he sits in a specialized tent for regular 30-minute sessions in order to get away from it all — sending sales of the EMF-shielding tent, made by Missouri-based SaunaSpace, through the roof, according to reports.

“If I were to bring my phone in there, for instance, there’s no signal whatsoever. There’s no radiation EMF from power, from Wi-Fi, from cellular,” Dorsey said on a fitness podcast in March.

While most of these newfangled products are a small business reality, some big names are catching on. Watch company Timex Group, for example, is new to the game with a watch that claims to block radiation from electronics. The product, which costs between $600 to $1,500, will be sold by Saks Fifth Avenue and Neiman Marcus, starting in September, Timex execs said.

The reason for the increase is simple — technology is everywhere and people are afraid it’s ruining their health in ways they don’t yet realize, experts said.

“They don’t buy that it’s just stress anymore,” explained James Finn, founder of Elexana, a Manhattan-based EMF consultancy. “Insomnia is on the rise and more people are looking for answers.”

That is helping boost sales for Lucy Blyth’s magnetic discs, which claim to act as an EMF filter. Sales for the little wafers have doubled in the past 12 months, said Blyth. “We are at the same spot that the organic movement was about 15 years ago. I get a lot of moms coming to us with concerns about their kids using technology.”

Of course, the science behind such products is murky at best — and no company can claim that its products are effective without running afoul of the Federal Trade Commission’s false advertising policies or the Food and Drug Administration, which has not approved them for health purposes.

That’s why Timex, which sells Timex, Nautica and Guess watches, claims its Teslar watch “may” reduce stress caused by electronics or “enhance immune response in the presence of EMF,” according to marketing materials.

The central feature of the Teslar line is a copper chip, which emits an impulse that “generates a biofield around our bodies,” explained Paolo Marai, chief executive of Timex Group Luxury Division.

At a demonstration in July, the company tested people’s stress levels before and after wearing the watch using a biometric device. But they failed to prove their effectiveness as the first few volunteers were “too relaxed” — resulting in the audience losing interest.

“You are really in good shape,” said Enrico Margaritelli, chief executive of Teslar, a 30 year-old technology company with which Timex has a licensing deal, to one volunteer. “It looks like you are the worst example.”

“I’m skeptical about most of these devices,” said Finn, the EMF consultant, who has seen his business grow fivefold over the last year. Finn says there are common-sense solutions, like keeping electronics out of the bedroom and turning off WiFi routers at night.

Still, he see more large companies selling products to block EMF as Americans continue to fret about the unknown impact of technology on our health.

“I could see 3M coming out with a film to apply to windows,” he said of the maker of tape. “Or other companies making sleep canopies.”