BOULDER - Energy-efficient window maker Alpen High Performance Products LLC has bought back its local window and architectural glass operation from Serious Energy Inc. of Sunnyvale, California.

Financial terms of the deal were not disclosed.

Boulder-based Alpen has two local manufacturing plants with more than 50 employees, said Brad Begin, the company's chief executive. Alpen was founded in 1981 in Colorado. Company assets were sold to Serious Materials, the predecessor of Serious Energy Inc., in 2008, and now have been bought back, Begin said.

"We're very excited about the future. The company is very strong right now," Begin said. "We produce a high-quality product that is having great success in the marketplace."

Insulated glass and windows are made at the two Boulder facilities and shipped to 100 dealers around the nation. Locally, the windows and glass have been used in thousands of projects, including several McDonald's restaurant Playland facilities and at the Denver Zoo, Begin said.

Alpen glass products have some of the highest insulating properties of any glass available in the nation, Begin said. The glass is used to promote solar control in homes and businesses, he said.

Nationally, projects include four Smithsonian Institution museums, the National Gallery of Art and the Empire State Building in New York City, among others, according to a company press statement.