A couple of months ago at a weaver's meeting, someone asked the group for a solution to a floating selvedge that was constantly breaking. In the back of my mind, I remembered a paper that Alice Schlein had written about the subject for the Complex Weavers CADE study group, but couldn’t really recall the details well enough to give an answer at that time. As these things go, I had a warp with floating selvedges on my loom and the one on the right side started unplying and breaking frequently. I looked up my copy of Alice’s article and found that she has a pretty good answer to the problem and one that you aren’t going to find with a Google search.
Alice explains that when your shuttle goes over a plied thread, it either increases or decreases the twist. If you decrease the twist enough, it eventually frays and breaks. The solution Alice proposed is to determine whether your selvedge thread has been plied S or Z. Most commercial yarns are plied S and you can check yours with a hand magnifier if necessary. If your yarn has been plied S, you will pass your shuttle over both floating selvedges when your shuttle travels from left to right and under both of them on the return trip from right to left. If your floating selvedge yarn is plied Z, then you reverse these instructions by going under both floaters from left to right and over when you throw the shuttle right to left.
It takes a bit of time to learn this technique of going over or under both threads, but after you have practiced a while, everything falls into place and your selvedges look better too.
While doing my online research about this subject, I found that many people recommended a temple, which helps if there is too much draw in from your reed to the fell line. But I am firmly convinced that Alice's explanation is really the answer to selvedge breakage on one side of your warp.
Reference: Schlein, Alice. "The Selvedge Dilemma: Dealing with Breakage" Complex Weavers Computer Aided Design Exchange. October, 2003