AMSTERDAM, June 28 (Reuters) - Dutch health technology company Philips said on Tuesday that it had seen "very encouraging" results from independent tests on the ventilators it recalled last year due to concerns over potential health risks from a type of foam used in the devices.

The tests showed foam degradation almost exclusively in machines that were cleaned with unauthorised ozon-based products, Chief Executive Frans van Houten said.

"What we have seen is that foam degradation is very rare", Van Houten told Reuters in a telephone interview.

"Inspection of over 60,000 machines in the U.S. has shown foam degradation in less than 0.5% of the machines users said had not been cleaned with ozon." (Reporting by Bart Meijer, Editing by Louise Heavens)