Eddie Yu's friends thought he was crazy when he sold his successful face mask start-up to launch a new business in 2021.

He'd founded Maskology in the early days of the pandemic as people scrambled to buy masks amid a shortage and fear of the emerging virus. Yu built it into a well-known and popular local brand, as Hongkongers snapped up keenly-priced, locally-made face masks.

He wasn't the only one with the same idea. According to the Hong Kong Mask and PPE Organisation (HKMPPE), at its peak in 2020 the industry had around 200 mask factories and brands as a mask became a daily necessity.

But Yu changed focus a year into the pandemic, amid a glut of supply in the market, and after a discussion about the environment with his niece. He walked away from Maskology and set out to develop the world's first plastic-free, biodegradable mask.

"When there's an oversupply [of masks], we already knew that our job is done...Covid will be gone one day, and the consumers will stop wearing masks one day. We are, well before, prepared to make the change," he told RTHK. "The market share of biodegradable face masks, which can be used in hospitals, is actually zero. So if we talk about the business, it is a huge market."

While Yu found success, others floundered. By the end of 2021, fewer than 50 factories were left, and the number of manufacturers dropped further to about 20 last year.

And while Yu was ahead of the game in switching to a new niche, other businesses in the sector are facing the challenge of finding a way to survive when their products are no longer a daily necessity.

The requirement to wear face masks in public, in place since July 2020, is one of the few Covid restrictions yet to be lifted. But officials have indicated that the days of mandatory masks are numbered ... at least outdoors.

The HKMPPE says it understands about a dozen factories will still continue to operate this year, despite the likely dwindling demand.

Its chairwoman, Dana Wu, urged the authorities to provide financial assistance to the mask manufacturing industry, along the lines of a subsidy scheme introduced to kick-start local production when masks were in short supply in 2020. Government support for local mask production lines ended in June 2021.

"We are needed, and we are valuable to stay and survive in Hong Kong, because we don't know how many diseases will come in the future. But these three years, we already built this industry in Hong Kong, and we can supply all of our customers, all of our citizens," Wu said, adding that remaining brands have diversified their business to launch other products such as disinfectants.

For local brand SAVEWO, which owns a 140,000 square foot factory in Tsuen Wan, the future lies in pivoting its production to cater mainly for the medical sector.

"We will do more medical respirators. If the demand is really low some years later, maybe we will slow down the production," co-founder Melanie Choi said.

"If the government and corporations have a mind to support local businesses and use local masks, sourcing the masks from Hong Kong instead of [mainland] China or other parts of the world, we may still have a way to survive," she added.

But Dennis Ho, the founder of Acc+, a brand that works with a factory in Taiwan to make face masks, remains hopeful.

"After a few years of wearing masks, there is a habit from the public. We think some of the people will keep on wearing a mask to protect themselves and their families. The demand will not be higher than Covid, but must be higher than three years ago," Ho said.

"As a company selling masks, we should adapt to any change in the environment and find other suitable products for the customers. We can't be stubborn," he added.

As for Yu, he says his new company, ÖKOSIX, has another advantage over its rivals. As well as making its masks compostable, it's also become a supplier of materials, and is working with Hong Kong Science and Technology Parks to develop its business.

"We entered Science Park because the technology we developed can not only be used in face masks, but also used in diapers, sanitary napkins and air filters. So we are actually opening more industries for us," he said.

"I believe only the strong players will remain...There are a lot of brands which will still supply face masks in Hong Kong, because hospitals have been using [them], clinics and factories [as well], but maybe a lot of masks will not be made in Hong Kong any more."