Hi Mitch:
I purchased the recycled fabric for my Firefly but I have yet to cover the kayak. I bought an extra yard of fabric and have been experimenting with shrinking techniques and various paints on 1 foot square frames.
I once rebuilt and covered a small airplane with polyester fabric so I pulled out the manual for a refresher (understanding that aircraft fabric and our recycled fabric are probably two different animals, aircraft fabric is typically 2.7 oz …but polyester is polyester). The manual specifies an initial shrinking at 250 degrees with a calibrated iron to obtain a uniform tension (prevents warping of the wing and pulling on the ribs). The final temperature to develop maximum tension is 350 degrees. The manual warns “…polyester filaments will start to thermo-soften and loose measurable tension at about 375 degrees…”.
I used this technique on one of the test panels with good results. I guess this is my long-winded way of saying, shrinking at a higher temperature may be a solution. Notice I said “may”…who knows, the recycled fabric may give up, over time, some of it’s tension regardless of temperature used for shrinking.
I hope this is helpful and I will let you know how things turn out with my kayak….