There was an in-depth discussion on he Greenland Paddling site years back about fabric. Dacron shrinks less with heat but also holds it's tension better than Nylon. Nylon shrinks more and with less heat but once wet looses it tension more. I have only built one DOF and used Dacron and it held it's tension great. I pulled it quite tight when skinning it as well. A good tool that helps that is an artist canvas pliers with the wide flat jaws. It's fairly cheap on Amazon or art stores.

The bulk of the people building SOFs seem to always use Nylon. Maybe because it easier to find??? I think Nylon is a tiny bit easier to pull and bend. The Dyson Dacron I used was quite tough. It was the middle weight. I can't remember the exact weight since it was quite a few years back. I didn't own a heat gun and just ran over mine with a propane torch which is also good for sealing the edge fabric. When it was done you could bounce a dime on it. It will loosen but not like I've seen on some Nylon ones that just start sagging especially when wet..