(NEXSTAR) – In 2020, Lego saw sales grow over 20% compared to 2019, with the year’s revenue reaching 43.7 billion Danish krone, equivalent to roughly $6.99 billion. Those kits could end up providing more than just entertainment for some.

A new study out of Moscow found discontinued Lego sets can have more value than stocks, bonds, gold, and other traditional investments like art. Researchers reviewed the prices of over 2,300 Lego sets from 1987 to 2015 and found that they appreciated in value by roughly 11% each year, outperforming “traditional” investments.

Two or three years after a Lego set is retired, researchers found the secondary market prices usually start to grow. Kits that are small and those that are very large grow faster in price compared to medium-sized ones. This, researchers believe, is due to small sets containing more unique parts or figures. For the larger kits, fewer are produced, making them harder to find.

The study, published in the Research in International Business and Finance journal, also found that Lego kits dedicated to famous buildings, movies, or holidays tend to see the most appreciation. Lego sets issued in limited editions or available at promotional events also tended to increase in value due to their rarity.

Researchers found some of the most expensive Lego sets include those from the Star Wars series – the Millennium Falcon, Death Star II, and Imperial Star Destroyer. Another, the Cafe Corner, saw a return of 2,230% from the time it was released in 2007 to 2015.

“Investors in LEGO generate high returns from reselling unpacked sets, particularly rare ones, which were produced in limited editions or a long time ago. Sets produced 20-30 years ago make LEGO fans nostalgic, and prices for them go through the roof. But despite the high profitability of LEGO sets on the secondary market in general, not all sets are equally successful, and one must be a real LEGO fan to sort out the market nuances and see the investment potential in a particular set,” Victoria Dobrynskaya, one of the researchers, said.

Researchers add that while Lego sets can have a large payoff, the investment is only worthwhile in the long run and can be costly thanks to delivery and storage.

If you haven’t accumulated sets upon sets of Legos, you aren’t out of the running for making some money on your old toys. Some of your other childhood favorites could have value in the collectibles market.

“For a toy to be collectible and have value on the secondary market, there has to be an emotional attachment to it. It conjures up a memory,” Jordan Hembrough, toy expert and host of the show “Toy Hunter,” tells Nexstar. He recommends checking your attic or your old toy bin – old characters are gaining popularity and toys from decades ago are once again becoming valuable.