Enact's investment will grow Excelsior in Europe and the US. The firm currently employs 240 staff with 180 people in Deeside, North Wales; and 60 people in Nelson, Lancashire, UK.
Chris Cormack, who manages the Enact fund on behalf of Endless will be joining the Excelsior board.
Enact is a £7.5m EIS fund that has been launched officially by Endless last year. It provides equity investments of between £250,000 and £2m to SMEs.
"Excelsior needs additional funding to allow it to grow its business, and our understanding of the packaging sector will enable Endless to contribute to strategy as well as to provide funding," he said.
Nick Alexander, CEO, Excelsior said the company has seen good growth in Europe and the US in recent years and has plans to grow further.
“This investment by the Endless Enact Fund, along with an agreed enlargement of our RBS facility, will make significant resources available for investment and to fund additional working capital," he added.