Spun Polyester is the most durable American flag on the market. The open weave reduces fabric stress and resists high winds. These flags are the best choice if you fly the flag 24/7 and your wind speed is higher. As these flags are made from heavier fabric they require a higher wind speed to "fly" than nylon flags. Also they require more effort to put up and take down.
Koralex II looks like a coarse cotton. 100% US made, with sewn stripes and embroidered stars. Designed for outdoor use, resists fading and fraying. Canvas or nylon headings and brass grommets.