Originally Posted by dd
So why does cutting the same fabric on the bias make it last longer than on the straight of grain? I don't understand that one.
The theory is that with the bias cut on the straight of grain, the wear is concentrated on a couple of threads that run along the edge of the binding. If one of these threads is damaged at one point, it could be compromised along its entire length. With the binding cut on the bias, each individual thread in the fabric runs through the binding strip only a short distance and if damaged will not cause the entire binding to be compromised. There are still pro's and con's about using bias binding (unless you have a curved quilt edge, and then you need it).
oops...I see that glassquilt already answered the question while I was thinking of how to explain it.