In 2010, the audio producer Roman Mars launched 99% Invisible, a podcast about the hidden designs and inventions most of us overlook. At the time, he didn’t have high hopes for it. Not only was the subject matter wilfully niche – early topics included building acoustics and the ergonomics of the toothbrush – but the episodes were just four minutes long. Still, listener numbers quickly grew and the episodes got longer. Sixteen years on, 99% Invisible is now a podcasting institution that has amassed more than 660 episodes, investigating everything from political logos to the colour of margarine. “It’s taking something that seems really boring and going, ‘No, no, no, this is interesting,’ and really convincing you of that,” Mars says.

Mars, 51, is talking over video call from a small, foam-panelled studio at his home in Berkeley, northern California, where he records the show. His voice – warm, mellifluous, gently quizzical – is synonymous with a particular American podcasting style that is erudite yet informal. There’s a reason why Mars habitually talks close to the microphone rather than declaiming from a distance. The effect is to make listeners feel as if he’s broadcasting from the inside of their heads.

This month, Mars is launching another pod project. A History of the United States in 100 Objects is a co-production between BBC Studios and 99% Invisible, and a sequel of sorts to the series A History of the World in 100 Objects, which aired on Radio 4 in 2010. Timed to coincide with the 250th anniversary of the US Declaration of Independence, Mars’s series comprises 100 episodes airing across two years, each of them highlighting objects and designs that tell the broader story of the United States.

When BBC producers first came up with the idea, someone would suggest an object, only to discover 99% Invisible had already made an episode on it. Eventually, they called up Mars and asked him to front the series; he didn’t hesitate in saying yes. “After years of doing 99% Invisible, and using design as a lens to look at things, it’s nice to approach it a bit differently and look at certain objects and ask: what does this say about America?”

Among the early themes is the screw thread, the spiral groove on screws that allows metal-on-metal fastening, and its standardisation across the industrial US and, later, the world. “It is the perfect object,” says Mars, “because it is completely overlooked, yet it explains so much about what modern day US imperialism is all about.” Elsewhere, there will be stories about the Bundy Clock, used by shift workers to punch in and out; a gold coin recovered from the SS Central America, which sank in 1857 and sparked a gold crisis; and the Billy Possum, a soft toy named after president William Howard Taft that tried and failed to replace the Teddy Roosevelt-inspired teddy bear.

For Mars, the experience of researching the series has been akin to “putting myself through an American Studies major”. Finding out if a story has legs requires many hours of research. “I’m always reading three books at once and listening to audiobooks at double speed while walking my dog.”

A career in audio wasn’t originally the plan for Mars who, encouraged by his teachers, left high school at 15 to do a degree in biology. After graduating at 19, he started a PhD in plant genetics; his specialism was the genetic makeup of corn. He soon realised he “wanted to study new things all the time. So I dropped out. For a while I thought I might be a science teacher. But all through my [education] I had been listening to radio, and so I had this idea that maybe I could explain things on radio shows.”

After production gigs at public radio stations in San Francisco and Chicago, as well as on the long-running NPR series Snap Judgment, Mars masterminded 99% Invisible, which was named after a quote from the American architect and systems theorist Buckminster Fuller: “Ninety-nine percent of who you are is invisible and untouchable.” For the first few years, he made the show alone; now he has a fleet of staff, many of whom have launched their own miniseries on the 99% Invisible feed.

Mars doesn’t believe his broadcasting career would have taken off were it not for the rise of podcasting. He notes that his voice isn’t a good fit for traditional radio, which prefers a clear and clipped tone as opposed to the mellow Mars vibe. Nonetheless, he says: “I found my voice and I became very relaxed behind the microphone. Now I am more comfortable talking into a microphone than I am talking to humans.”

Is he dismayed by the rise of video podcasts and their encroachment into what was previously an audio space? Mars sighs: “I just think it’s way more interesting to make the best possible audio show than the shittiest television show.”

No surprise, then, that 100 Objects and 99% Invisible are proud audio-only productions. “These are documentary shows where we put a bunch of people’s voices together in different ways. It couldn’t work any other way,” notes Mars. “To suddenly have my face in there? It’s not me. I prefer to be the voice in your head.”

Life from Mars: objects featured in the podcast

The Bundy Clock
“The Bundy Clock was the first employee time clock – introducing the idea of clocking in and out. But it also represented a change in how we measure work and our value as human beings, as we shifted towards the gospel of efficiency. The ghost of Bundy’s time-clock is everywhere. It is so ubiquitous, so ingrained in our psyche, yet shockingly little, beyond obscure academia, has been written on it. It encapsulates a lot about American labour: our push to turn workers into machines, and how we commodify time. ‘Time is money’ was literally carved into the wood of Bundy’s clocks.”

A gold coin from the sinking of the SS Central America (main image)
“The 1857 Ship of Gold sank in a hurricane off the US east coast, carrying hundreds of millions of dollars of gold,” says Mars. “After eight years of the gold boom, the economy was overheating and New York banks were waiting for that gold to shore up their coffers. The ship sank, carrying with it hundreds of lives and millions of dollars, leading in part to the panic of 1857, the first truly global financial crisis. It took 100 years for the ship to be found, but when the treasure hunter arrived with the gold, he was hit with lawsuit after lawsuit; he ultimately went to prison rather than reveal the location of the final coins.”

The 60-degree screw
“[The actor] Daniel Radcliffe and I share two things in common: excellent beards and we both love Daniel Immerwahr’s How to Hide an Empire. One of Radcliffe’s favourite books, it’s the story of how the US built a hidden empire by standardising screws. Before the mid-20th century, stop lights weren’t standardised: you stopped on green in Manhattan and on red in upstate New York. And hoses and fire hydrants didn’t always fit: fire engines would arrive unable to get water. Each machine used a slightly different screw. When the second world war broke out, we learned the danger of not being compatible with the rest of the world. The lack of standardisation of screws was a disaster. As factories in Europe were decimated, the US took on more war manufacturing. Eventually the world retooled their economies to the US’s preferred screw, remaking all machinery to fit it.”

The Century Safe
“One of my all-time favourite historians, Jill Lepore, gave us a gift when she wrote about the Century Safe. It makes the perfect object #1. It was a time capsule, sealed in 1876 and opened by the president during the bicentennial celebrations of 1976. Inside the safe were supposed to be meaningful objects: objects to tell the story of our country. Instead, when they opened it, completely random and meaningless objects fell out. It’s a humbling story about how hard it is to tell our own story and the impossible challenge of choosing objects to represent our history.”

Webster’s Blue-Backed speller
“Building off a chapter in Imani Perry’s Black in Blues, we have the story of a schoolbook so common it was basically wallpaper, until newly freed Black Americans turned it into an instrument of liberation. We track how it travelled from white schools into the hands of people for whom reading was an act of defiance, and meet two towering figures, Booker T Washington and WEB Du Bois, who each have pivotal experiences with the Blue-Back.”

The Billy Possum
“This is a story of two stuffed animals: one you’ve heard of, one you definitely haven’t. When Teddy Roosevelt’s decision to spare a bear’s life was memorialised in a political cartoon, enterprising toy-makers turned the story into a blockbuster stuffed animal, dubbed Teddy’s Bear. The teddy bear became a symbol: we had feared the bears, we had tried to eradicate the bears, and now we wanted to give the bears a hug. The Billy Possum – its failed stuffed toy follow-up, named after presidential successor William Howard Taft – demonstrates how our stories about animals can turn them into powerful symbols, or not.”

A History of the United States in 100 Objects will be released weekly from 19 May on BBC Sounds and 99% Invisible.