Toys aren't just a business for kids, they're also for adults. One kind of toy called Blind Boxes is becoming very popular with adults. You buy small figurines packed in a box, without knowing just what they are. The thrill is in opening the box - and then in trading and collecting all the designs you can.

The Blind Box business originated in Japan and is now becoming more visible in China. While with an average of 60 yuan (about 8.4 U.S. dollars) for one, shops selling these toys do not lack customers. It is a game of luck! In the most popular boxes, Sony Angel dolls for example, each series has 12 designs and one easter egg that's a secret design. Usually there's only one in a box of 144 boxes. But that's not the only thing adding to the thrill.

A store manager Yang Jia said toymakers usually come up with new basic designs every three months and have limited editions for holidays. And there are also limited editions for different cities to attract more attention.

Meanwhile, the second-hand market for Blind Boxes is also a big hit. Yvonne Chen is a big-time collector – she's been buying them for more than a decade now, usually spending around 2,000 yuan a month on the little statues. And she said the circle of doll dealers and traders keeps getting bigger and bigger.

"If I really want some particular doll and can't get it with my boxes, I'll buy it from other collectors, usually for around 600 or 700 yuan a piece. But just the usual designs sell at a discount to that," she added.

A report by China's largest second-hand trading platform Xianyu showed that in the past year, there were some 300,000 Blind Box collectors trading on its platform. And the most popular dolls now sell for almost 40 times their original price. Jason Yu, managing director of Kantar said the sense of excitement stimulate young people to buy so that it drives the market.

"These Blind Boxes, they usually charge like 50 RMB, so most of the young people they can afford it… It's like a lucky draw, so it's very exciting, creating a sense of excitement and investigation. Also on social media, and people can share it, like on WeChat, so it creates a sense of belonging," he said. "But honestly speaking, I think the demand need to be sensibly measured, the figure itself doesn't contain much value, it's more the sentiment behind those collections.”

Still, toymakers continue to see great potential in the market. During the last Double 11 sales gala, Pop Mart, one major player in the Blind Box business, sold some 27 million yuan worth of the little things, and now there are even online apps that let you pay for a box.