TOKYO -- Japanese biotech startup Spiber has raised 5 billion yen ($44.1 million) to build a facility in Thailand for mass-producing synthetic spider silk protein.

The proprietary protein is made into a durable, eco-friendly thread that can be used to produce a variety of products, including clothes, medical equipment and auto parts.

The money was raised from the public-private Cool Japan Fund and other investors, pushing Spiber's capital to 22.4 billion yen, one of the highest among unlisted Japanese startups.

Spiber plans to produce several hundred tons of the protein annually at the new plant. "The production capacity at our Thai plant will be 100 times larger than that of our Japanese pilot plant, and one of the world's largest," said Representative Executive Officer Kazuhide Sekiyama.

Thailand has ample supplies of the biomass resources needed for the production process. The country is also a major hub for makers of apparel and automobiles, two of Spiber's key targets.

The startup was established in 2007 to advance research on synthetic spider silk by Keio University's Institute for Advanced Biosciences. Located in the city of Tsuruoka in Yamagata Prefecture, the company was the first to perfect technology for mass-producing the synthetic protein, which is then spun into thread that is four times stronger than steel but more flexible than nylon.

The high price of manufacturing the protein material, trademarked as Qmonos, has thus far hindered commercialization, but Sekiyama said he expects to reduce costs to between $40 and $50 per kilogram.

(Video released in February 2015)

Construction of the Thai facility will start by mid-2019, with production slated to begin in 2021. Protein made there will be processed into thread at the company's Japanese spinning plant in Yamagata.

"Earth-friendly, synthetic spider silk protein could become a next-generation base material," said Yuji Kato, chief operating officer of Cool Japan Fund.

Sekiyama claims that Qmonos can be used in a wide range of industries. "We hope it can satisfy 15% to 20% of total [global] fiber demand," he said.

In September, Spiber allocated 5 billion yen worth of new shares to third parties, of which about 3 billion yen were underwritten by Cool Japan Fund. The company did not disclose other investors, but Sekiyama said that "five or fewer companies were included as strategic partners for joint development."

Spiber, which has about 200 employees, is seen as one of Japan's potential unicorns -- unlisted ventures with a valuation of $1 billion or more.

Sekiyama said he still does not consider his company a unicorn in terms of valuation even after the latest funding, but that he is considering an initial public offering as a way to raise more money in the future.