The world of sports cards is on fire, as evidenced this month by a LeBron James rookie card – specifically his 2003-04 Upper Deck Exquisite autographed patch card, one of only 23 produced – which recently sold at auction for $1.8 million. That nearly doubles the record for a modern-day sports card, which had been set mere months ago in May, when a Mike Trout rookie card went for $922,000.

But it’s not just the modern-day cards that have seen wild price increases, and it’s not just wild price increases that are being seen. In fact, according to the PWCC 500, investing in high-grade sports cards has been a significantly better investment than investing in the S&P 500, and this has been true for years.

So who is part of this over $5 billion market? About 6% of the American population, as it turns out – and nearly a third used to collect.

The same amount – 6% – are involved in the investment angle when it comes to sports cards

Of that group, a few notable numbers pop out: It’s dominated by Gen Z and the 25-34 age brackets, wealthier households are more likely to have someone who at least dabbles in the investment portion of sports card collecting, and men are twice as likely as women to invest in sports cards.

Of course, as with any business, the producers – in this case, Topps, Panini, Upper Deck, and a handful of other, smaller operations – would love to see this market grow.

How to do so? Nostalgia is one way to go, as 35% of current sports card collectors name that as the main reason they buy sports cards.

But even more American collectors – 38% to be precise – collect either to resell or to invest.

Men are more likely to have dabbled in collecting, but nearly a quarter of women either currently do or have collected in the past.

And when it comes to income, this is an area where the manufacturers – and the secondary market sellers – can really start to reel back some old customers, as people in households making over $100,000 a year are 30% more likely to have someone in it who used to collect cards.

And let’s not forget the money to be made in the whole “buy low, sell high” end of things.

For instance, people who say they pay some attention to their stock market are 40% more likely to have collected sports cards than people who pay no mind to the stock market, and 43% more likely to have collected than people who don’t have any stock investments.

This line of reasoning also bleeds into art, with people who used to collect sports cards being 38% more likely to be at least somewhat interested in modern art than people who never collected.

Sports cards are still considered by many to be a childhood obsession, not something for serious-minded investors. But clearly, the market is saying otherwise. With only 6% of the population actively collecting cards of any sort, there is clearly room for growth. And instead of advertising to the ones already singing their tune, perhaps the manufacturers and re-sellers should be looking at the back pages of the Wall Street Journal or American Art Collector.