Armacell has attracted interest from other private equity groups, the sources said, with Blackstone (>> Blackstone Group LP), Carlyle (>> The Carlyle Group LP), CVC [CVC.UL], KKR (>> KKR & Co. L.P.) or TowerBrook cited as potential bidders, as well as industrial groups, the sources said.

The company could be worth up to 10 times its expected core earnings this year of roughly 100 million euros, one source said, while others said an earnings multiple of 8-9 times core earnings was a more likely valuation.

Armacell's peers such as Rockwool (>> Rockwool International A/S) or Kingspan (>> Kingspan Group plc) trade at an average multiple of 8.7 and 13.5 times their expected earnings, respectively.

After initially launching preparations for a stock market listing of Armacell last year, Charterhouse recently opted for a sales process led by investment bank Rothschild [ROT.UL].

Armacell in 2014 posted adjusted earnings before interest, taxes, depreciation, and amortisation (EBITDA) of 71.2 million on sales of 452 million euros.

Charterhouse bought Armacell from Bahrain-based private equity firm Investcorp for over 500 million euros in 2013.

Armacell, which is based in Muenster, Germany, and operates 23 manufacturing facilities around the world, has 2,600 employees and says it is the world's largest maker of flexible insulation, making products used to lag pipes and ductwork in factories and schools.

Charterhouse, Rothschild and the other private equity groups declined to comment, except for CVC, which was not immediately available for comment.

(Reporting by Arno Schuetze; Editing by Andreas Cremer and Adrian Croft)