Hiding in a closet or box of old clothing (or even on your baby right now!) could be one of the prized suits that sell for hundreds of dollars online, particularly if it was never worn. Collectors call them "unicorns" and speculation is driving value up to ten times the retail price.

The secondary Bonds market first made headlines this year when a Confetti pattern suit appeared to sell for $60,000, although this turned out to be a hoax price. Most suits resell for less than $50, but many sell for over $100 and collectors have told Fairfax Media they are now hoarding Wondersuits and hoping for higher prices.

(To those unfamiliar with Wondersuits, they are a one-piece long-sleeved and long-legged zip-up baby suit with double cuffs and sleeves that can be folded over to keep little hands and feet warm.)

Ashley Cullens has amassed about 70 Wondersuits since she started collecting them for daughters Ava, 3, and Harper, six months, to wear.

Taken by the different colours and patterns, and the convenience of the two-way zip, she buys a Wondersuit most days and once spent $60 on a rare Paisley edition. "I've got them in all sizes from 000 to size 3," the Sydney mother said. "It just sort of became an addiction."

Ms Cullens is starting a boy's collection in case her family grows. She sees the suits as an investment. "I probably will keep them because they'll end up being rare ... unless the addiction for everyone just crashes and I'm stuck with all these Wondersuits."

The head of marketing at Pacific Brands, which owns Bonds, Emily Small, said it is "very aware" of the secondary market for zip-up Wondersuits and enjoys the high demand. "We sell one zippy suit every three minutes," she says.

Bonds releases several new designs every year for summer and winter and does not generally repeat patterns. The volume of suits manufactured with each print varies. Asked if Bonds would ever repeat the most prized patterns, Ms Small said Pacific Brands is not really a competitor to the secondary market and is a "manufacturing business putting a great product out into the marketplace".

The famous Confetti design is a limited-edition pattern released for Christmas 2014. An unworn one was this week listed for $149 on eBay, which is a 583 per cent increase on the purchase price. A size 2 suit recently sold for $202. As far as investments go, it's not a bad return.

Along with Confetti, a bright-pink cherry design for girls is also popular, and a white floral design on a blue background called Native Crown, and a purple suit with strawberries, which goes for as much as $180 unworn.

Melbourne mother Aleda While noticed a blue boy's Wondersuit with a black truck pattern in high demand online. She had one sitting in a cupboard that she received as a gift several years ago. Within 10 minutes of listing it on eBay she had sold it for $100 to a woman in Sydney "just because it was a size 3 and a rare print", she explains.

One woman recently paid $50 – double the retail price – for a Salmon Paisley suit through a Facebook group. Asked why, she said "because it was new as I have bought preloved and people overstate to get more money and they sometimes smell and the other reason was that one is just beautiful".

She also explained the scarcity by adding "I am pretty sure its a 2013 print and I live in a shitty rural town where Bonds stock is next to non-existent". She plans to "squeeze" her older children into the suit for themed Christmas portraits.

The administrator of a Bonds buy/sell/swap Facebook group, Steven Wayne, says Wondersuit collecting was "an absolute epidemic at the moment".

"I think it always used to be people were buying these for their kids to wear. Now I think you are seeing a bit of a change where people are buying them to collect because they are increasing in value. You can clearly see that happening with the way Bonds [suits] are selling out online and in some shops," he says.

He has bought 35 Wondersuits in the past five months, including a Confetti suit, which he has carefully stored in plastic with all the tags attached. He hopes they will become unicorns, fetching big dollars. Any design that has a limited release or is made exclusively for one store, such as Target, could become a unicorn, he adds.

Bonds' baby range is designed in Sydney and manufactured in China and Cambodia. Wondersuits retail for about $22 apiece and Pacific Brands sells up to 175,000 units every year. The zip feature was first introduced in 2012. Wondersuits becoming collectible is reminiscent of Beanie Babies, a soft toy released in the 1990s. The toys have remained popular with collectors and can still fetch thousands of dollars.