In the 2009 Edition of Plumbing & HVAC Product News Roy Collver makes the following statement in his article Fantastic Plastic.
“In researching the venting issue I asked a number of engineering types what their material of choice would be for venting gas appliances. To a person, they all had the same answer – POLYPROPYLENE!”
Roy had worked for many decades in all facets of the industry and is a frequent magazine contributor.
He had another article published in the March 2011 issue that also focused on PP venting entitles, “Ready for Prime Time”.