Original poster: "Ralph Zekelman" <gridleak-at-bluemarble-dot-net> Luke, It sounds like you bot the ducting with the crimped joints. Check out items in the range of McMaster-Carr 5525K46. This ducting is seamless and handles like an accordion. 2.5 feet will stretch out to 30ft. I have used it with excellent results for toroids as small as 16 inches. No tearing. Ralph Zekelman