|This is a weaving trick for sett used in industry: a balanced looking fabric is actually a bit more warp predominant than precisely balanced. It looks balanced at a glance, but upon inspection, you will see that there are more warps per inch than wefts per inch. We handweavers can use this principle, too. And I almost always do when I want a generally balanced weave. The way to achieve this is to take 80% of the maximum sett using the Ashenhurst method.
Why it’s so wonderful to weave with a slightly closer warp sett:
In general, whenever I’m debating between two numbers for a sett, I’ll choose the denser number for the above reasons. That means, if I were debating between 6 and 8 epi, I’d tend to choose the higher number of 8. If I’m weaving an open shawl, however, I want it more open than the 80% number, for sure. Of course, my sample will be the ultimate test.
When you don’t want to use the 80% figure
You need to account for the texture of the thread when you are considering how low a sett to choose (minimum sett). Hairy yarns wouldn’t be good for the 80%. Woolens are meant to shrink, so the 80% wouldn’t work for them either. Smooth, slippery silk or rayon threads need to be sett closer than 80% (more warps per inch) than woolens because the slippery yarns will create unwanted spaces after you wash your cloth (called slippage), spaces that hairy yarns would fill up.
More information in Weaving for Beginners and Book #1: Winding a Warp & Using a Paddle.