The company, whose Scottish operation once supplied 10 million plastic mobile-phone cases a year to Motorola and Ericsson, is a supply-chain survivor of the turn-of-the-millenium "silicon glen" crash.
It now makes high-spec precision injection-moulded parts for diverse sectors including leading car makers, the food and drink industry, and manufacturers of business machines such as ATMs. Clients include Diageo, for whom Rosti makes canned Guinness "widgets", and Jaguar Land Rover.
The latter produces 400,000 vehicles a year, including the newly launched hybrid Land Rover Evoque, and they all contain Rosti's plastic parts.
Barry Coughlan, Rosti's chief operating officer for Europe, who is based at the firm's 10,000 square metre Larkhall plant, said the firm had "come back from the brink" to become the largest trade injection moulder in the UK, and was now "actively seeking new acquisitions".
Last year, advised by lawyer Burness Paull, Rosti bought £75 million Yorkshire and Wales-based engineered plastics firm McKechnie for £30.7m.
Rosti, owned by Swedish investment giant Nordstjernan, works with local schools to boost understanding of apprenticeship and engineering opportunities, and to promote the increasingly green credentials of the UK plastics industry which Coughlan said "did not have a great [environmental] reputation in the past".
The "highly competitive" Larkhall factory, which turns over £20m a year, is 30% powered by wind energy. Mark Ellis of Burness Paull, who advised on the McKechnie deal in June, said: "We're delighted that a deal of this calibre, with a number of international dimensions, was led by Barry from Scotland.
"It is great to see what a success the acquisition has been and that with the support of the parent company, Rosti is continuing to invest in the UK and beyond."
Named after its Danish founders Rolf Fahrenholtz and Stig Jørgensen in 1944, Rosti has been through several ownership changes and restructurings, and now employs 1100 people in the UK.