As the post points out, many faiths incorporate garments into their religious practice, from yarmulke-wearing Jews to habit-donning nuns. But temple garments seem to make Americans unusually curious—they're often referred to as "magic underwear" and said to have "magical" powers. When the shadow of Mitt Romney's undershirt showed up beneath his neatly pressed white-collar shirts during his 2012 presidential campaign, it sparked explainers, spectacle, and even mockery.

"Because they're concealed under the clothing, because the instruction is not to show them to other people, and Mormons consider them to be sacred, that automatically gives a kind of aura of mystery to them, of secretness," said Patrick Mason, the chair of religious studies at Claremont Graduate University. The garments are given to members during a private ceremony inside a Mormon temple which can only be attended by active Mormons, adding to the air of secrecy.

This has been the case since members started wearing the garments in the early 1840s under the guidance of the founder of the Church of Latter-day Saints, Joseph Smith. "Because Mormons practiced polygamy from the 1840s on, and they have this private ceremony, the faith seemed to be all about sex to the populace: Is this all about sex, or is this about Jesus?" said Philip Barlow, a professor of Mormon history and culture at Utah State University.

Even though most of American culture has evolved away from the reserved sexual mores of the nineteenth century, the garments are still a source of fascination, if only because of the many logistical questions involved. For example: Do Mormons wear lingerie when they have sex? Some do, says Mason, although he noted that "Mormons don't generally talk a lot about sex or underwear." Has the underwear been the same since it made its debut in 1844? Nope, says Mason; it used to be much longer and identical for women and men, "which obviously doesn't exactly work."

Or, for that matter, what does it really look like? That seems to be one of the questions that the LDS Church is trying to answer in releasing public information about the garments. "White symbolizes purity," the website says. "There is no insignia or rank. The most senior apostle and the newest member are indistinguishable when dressed in the same way. Men and women wear similar clothing." The video shows the everyday garments worn by both genders, which look like a plain white T-shirt and shorts, and a longer robe that's worn in religious ceremonies. While many Mormons find that the garments "stir the deepest feelings of the soul, motivate them to do good, even shape the course of a whole life of service," the site says, they're also pretty straightforward: "There is nothing magical or mystical about temple garments."

Even within the Church, though, the garments have an almost mythical aura. "People will tell stories about how the garments protected them from some kind of physical danger, stories about people who were in a fire and all the parts of their body were burned except where they had their garments on," Mason said. It's even said by some that "Joseph Smith was not wearing his garments when he was assassinated in 1844."