: Do you know if heavier but shrinkable aircraft polyesters are available or do
: you have an idea why the thinner stuff is so heat shrinkable and the
: thicker stuff isn't. Would it make any sense to double skin parts of the
: yak w/ thinner skin and yet maintain the shrinkability.

The 3.7 oz is the heavier stuff. The lightweight fabric is only 1.7 oz, and is designed for ultra-light aircraft. The "standard" aircraft fabric is 2.7 oz, and is designed for general aviation. The 3.7 oz is for "heavy duty" use, like crop dusters and for aerobatics.

I am getting ready to use the 3.7 oz on a Putz-style boat, and made some test panels. For coatings, I tried epoxy, acrylic latex paint, and Varathane. In some unscientific tests (like scraping against a cement block, impacts with the corner of the workbench, and stabbing with a screwdriver), both the paint and Varathane held up well - although the paint looked pretty bad from the cement block. The epoxy did not, especially in the workbench test, where it cracked and delaminated. An arts and crafts website said Varathane could be pigmented using acrylic paints, so I mixed the two and made another test panel. As expected, it works quite well. The workbench and screwdriver tests did leave indentations in the test panels, but remained watertight (and I hit the corner of the workbench hard enough to break the wood frame supporting the test panel).

The 3.7 oz fabric is quite strong. I plan on going with the Varathane/acrylic paint mixture for the first few coats, and straight Varathane for the final coats, since it hides scratches fairly well. By the way, Varathane also makes a decent fabric adhesive.

As for doubling the fabric, I don't know if it is really necessary judging from the test panels. I did get some dacron reinforcing tape and applied it to the stingers and around the cockpit area for added durability in possible wear points. The only area I might try doubling is right behind the cockpit, where I lean getting into and out of the boat. And there will be ash rub strips on the keel and sheers. Of course, only time will tell if it is truly stong enough. But considering the cost of the fabric, Varathane, and paint total less than $100, if it doesn't hold up, I'll just tear it off and reskin the boat with something else.